The class for formatting the node tree is not well written and has no algorithm, but it can be used.

Format the classified data fetched from the database, such as:

News
--Sports News
--Entertainment News
Finance
--Forex
--Finance

class tree
{

    /**Raw data*/
	public    $original;

    /**key name of id*/
    public    $id;

    /**父The key name of the parent id*/
    public    $parentId;

    /**id during initialization*/
    protected $initId;

    /**node level*/
    protected $thisLevel = 0;

    /**final tree*/
    protected $tree = array();


   /**
     * 构造函数
	 +------------------------------------------
	 * @access  public
	 +------------------------------------------
	 * @param   array    $original
 * Constructor
 +------------------------------------------------
 * @access public
 +------------------------------------------------
 * @ param array $original original data
 * @param string $id key name of id
 * @param string $parentId key name of parent id
 +------------------- -----------------------
 * @return void

	 * @param   string   $id
 * Initialization
 +------------------------------------------------
 * @ access public
 +------------------------------------------------
 * @param array $original Original data
 * @param string $id The key name of id
 * @param string $parentId The key name of parent id
 +-------------------------- -----------------------
 * @return void

	 * @param   string   $parentId    父
 * Get initial node
 +------------------------------------------------ ---
 * @access protected
 +---------------------------------------- ------
 * @param int $parentId The level of the initial node
 +---------------------------------- ---------------
 * @return array $parentTree

	 +------------------------------------------
	 * @return  void
	 */
    public function __construct($original='',$id='',$parentId='')
	{
          if($original && $id && $parentId)
		  {
		     $this->initialize($original,$id,$parentId);
		  }
    }


   /**
     * 初始化
	 +------------------------------------------
	 * @access  public
	 +------------------------------------------
	 * @param   array    $original
 * Get subtree
 +------------------------------------------------ ---
 * @access protected
 +---------------------------------------- ------
 * @param int $id node id
 * @param string $levelTag indentation mark
 +---------------------- --------------------------
 * @return void

	 * @param   string   $id
 * Get the level of the node
 +--------------------------------------------- -------
 * @access protected
 +------------------------------------------------ -------------
 * @param int $parentId The parent id of the node
 +------------------------ ------------------------
 * @return void

	 * @param   string   $parentId    父
 * Get the complete tree
 +--------------------------------------------- -------
 * @access public
 +------------------------------------------------ -------------
 * @param int $level From what level to get
 * @param string $levelTag Indent tag
 +------------- ------------------------------------
 * @return array $this->tree complete tree

	 +------------------------------------------
	 * @return  void
	 */
    public function initialize($original,$id,$parentId)
	{
          $this->original = $original;
		  $this->id       = $id;
		  $this->parentId = $parentId;
    }


   /**
     * 获取初始节点
	 +----------------------------------------------
	 * @access  protected
	 +----------------------------------------------
	 * @param   int      $parentId       初始&
	 +----------------------------------------------
	 * @return  array    $parentTree
	 */
    protected function getParentTree($parentId)
	{
		  $parentTree = array();

          foreach($this->original as $key=>$value)
		  {
		       if($value[$this->parentId] == $parentId)
			   {
				    array_push($parentTree,$value);
			   }
		  }

		  return $parentTree;
 	}


   /**&*/
    protected function getChildrenTree($id,$levelTag)
	{
		  foreach($this->original as $key=>$value)
		  {
		       if($id == $value[$this->parentId])
	           {
				   if($levelTag)
			       {
					   $this->getLevel($value[$this->parentId]);
				       $value['levelTag'] = str_repeat($levelTag,$this->thisLevel);
					   $this->thisLevel = 0;
   				   }
				   $this->tree[] = $value;
				   $this->getChildrenTree($value[$this->id],$levelTag);
		       }
		  }
 	}


   /**
     * 获取&🎜	 +-------------------------------------------------🎜	 * @access  protected🎜	 +-------------------------------------------------🎜	 * @param   int      $parentId        节点的父id🎜	 +-------------------------------------------------🎜	 * @return  void🎜	 */🎜    protected function getLevel($parentId)🎜	{🎜		  foreach($this->original as $key=>$value)🎜		  {🎜		       if($parentId == $value[$this->id] && $parentId != $this->initId)🎜	           {🎜				   $this->thisLevel++;🎜				   $this->getLevel($value[$this->parentId]);🎜		       }🎜		  }🎜   	}🎜🎜🎜   /**&*/🎜    public function getTree($parentId=0,$levelTag='')🎜	{🎜		  $this->initId = $parentId;🎜          $parentTree   = $this->getParentTree($parentId);🎜🎜   		  foreach($parentTree as $key=>$value)🎜		  {🎜			   $this->tree[] = $value;🎜		       $this->getChildrenTree($value[$this->id],$levelTag);🎜		  }🎜🎜		  return $this->tree;🎜  	}🎜🎜}




$conf =  array(
	       1 => array('id'=>'1','parentid'=>0,'name'=>'1'),
	       2 => array('id'=>'2','parentid'=>0,'name'=>'2'),
	       3 => array('id'=>'3','parentid'=>1,'name'=>'1-1'),
	       4 => array('id'=>'4','parentid'=>1,'name'=>'1-2'),
	       5 => array('id'=>'5','parentid'=>2,'name'=>'2-1'),
	       6 => array('id'=>'6','parentid'=>3,'name'=>'1-1-1'),
           7 => array('id'=>'7','parentid'=>4,'name'=>'1-2-1'),
		   8 => array('id'=>'8','parentid'=>5,'name'=>'2-1-1'),
		   9 => array('id'=>'9','parentid'=>8,'name'=>'2-1-1-1')
	       );

$tree = new tree($conf,'id','parentid');
$arr = $tree->getTree(0,'   ');
foreach($arr as $val)
{
  if($val['levelTag'])
  {
     echo $val['levelTag'].'|- ';
  }
  echo $val['name'].'';
}

?>

class tree
{

    /**Raw data*/
	public    $original;

    /**key name of id*/
    public    $id;

    /**父The key name of the parent id*/
    public    $parentId;

    /**id during initialization*/
    protected $initId;

    /**node level*/
    protected $thisLevel = 0;

    /**final tree*/
    protected $tree = array();


   /**
     * 构造函数
	 +------------------------------------------
	 * @access  public
	 +------------------------------------------
	 * @param   array    $original
 * Constructor
 +------------------------------------------------
 * @access public
 +------------------------------------------------
 * @ param array $original original data
 * @param string $id key name of id
 * @param string $parentId key name of parent id
 +------------------- -----------------------
 * @return void

	 * @param   string   $id
 * Initialization
 +------------------------------------------------
 * @ access public
 +------------------------------------------------
 * @param array $original Original data
 * @param string $id The key name of id
 * @param string $parentId The key name of parent id
 +-------------------------- -----------------------
 * @return void

	 * @param   string   $parentId    父
 * Get initial node
 +------------------------------------------------ ---
 * @access protected
 +---------------------------------------- ------
 * @param int $parentId The level of the initial node
 +---------------------------------- ---------------
 * @return array $parentTree

	 +------------------------------------------
	 * @return  void
	 */
    public function __construct($original='',$id='',$parentId='')
	{
          if($original && $id && $parentId)
		  {
		     $this->initialize($original,$id,$parentId);
		  }
    }


   /**
     * 初始化
	 +------------------------------------------
	 * @access  public
	 +------------------------------------------
	 * @param   array    $original
 * Get subtree
 +------------------------------------------------ ---
 * @access protected
 +---------------------------------------- ------
 * @param int $id node id
 * @param string $levelTag indentation mark
 +---------------------- --------------------------
 * @return void

	 * @param   string   $id
 * Get the level of the node
 +--------------------------------------------- -------
 * @access protected
 +------------------------------------------------ -------------
 * @param int $parentId The parent id of the node
 +------------------------ ------------------------
 * @return void

	 * @param   string   $parentId    父
 * Get the complete tree
 +--------------------------------------------- -------
 * @access public
 +------------------------------------------------ -------------
 * @param int $level From what level to get
 * @param string $levelTag Indent tag
 +------------- ------------------------------------
 * @return array $this->tree complete tree

	 +------------------------------------------
	 * @return  void
	 */
    public function initialize($original,$id,$parentId)
	{
          $this->original = $original;
		  $this->id       = $id;
		  $this->parentId = $parentId;
    }


   /**
     * 获取初始节点
	 +----------------------------------------------
	 * @access  protected
	 +----------------------------------------------
	 * @param   int      $parentId       初始&
	 +----------------------------------------------
	 * @return  array    $parentTree
	 */
    protected function getParentTree($parentId)
	{
		  $parentTree = array();

          foreach($this->original as $key=>$value)
		  {
		       if($value[$this->parentId] == $parentId)
			   {
				    array_push($parentTree,$value);
			   }
		  }

		  return $parentTree;
 	}


   /**&*/
    protected function getChildrenTree($id,$levelTag)
	{
		  foreach($this->original as $key=>$value)
		  {
		       if($id == $value[$this->parentId])
	           {
				   if($levelTag)
			       {
					   $this->getLevel($value[$this->parentId]);
				       $value['levelTag'] = str_repeat($levelTag,$this->thisLevel);
					   $this->thisLevel = 0;
   				   }
				   $this->tree[] = $value;
				   $this->getChildrenTree($value[$this->id],$levelTag);
		       }
		  }
 	}


   /**
     * 获取&🎜	 +-------------------------------------------------🎜	 * @access  protected🎜	 +-------------------------------------------------🎜	 * @param   int      $parentId        节点的父id🎜	 +-------------------------------------------------🎜	 * @return  void🎜	 */🎜    protected function getLevel($parentId)🎜	{🎜		  foreach($this->original as $key=>$value)🎜		  {🎜		       if($parentId == $value[$this->id] && $parentId != $this->initId)🎜	           {🎜				   $this->thisLevel++;🎜				   $this->getLevel($value[$this->parentId]);🎜		       }🎜		  }🎜   	}🎜🎜🎜   /**&*/🎜    public function getTree($parentId=0,$levelTag='')🎜	{🎜		  $this->initId = $parentId;🎜          $parentTree   = $this->getParentTree($parentId);🎜🎜   		  foreach($parentTree as $key=>$value)🎜		  {🎜			   $this->tree[] = $value;🎜		       $this->getChildrenTree($value[$this->id],$levelTag);🎜		  }🎜🎜		  return $this->tree;🎜  	}🎜🎜}




$conf =  array(
	       1 => array('id'=>'1','parentid'=>0,'name'=>'1'),
	       2 => array('id'=>'2','parentid'=>0,'name'=>'2'),
	       3 => array('id'=>'3','parentid'=>1,'name'=>'1-1'),
	       4 => array('id'=>'4','parentid'=>1,'name'=>'1-2'),
	       5 => array('id'=>'5','parentid'=>2,'name'=>'2-1'),
	       6 => array('id'=>'6','parentid'=>3,'name'=>'1-1-1'),
           7 => array('id'=>'7','parentid'=>4,'name'=>'1-2-1'),
		   8 => array('id'=>'8','parentid'=>5,'name'=>'2-1-1'),
		   9 => array('id'=>'9','parentid'=>8,'name'=>'2-1-1-1')
	       );

$tree = new tree($conf,'id','parentid');
$arr = $tree->getTree(0,'   ');
foreach($arr as $val)
{
  if($val['levelTag'])
  {
     echo $val['levelTag'].'|- ';
  }
  echo $val['name'].'';
}

?>