How does ThinkPhp output second- and third-level columns in a tree shape?

Question

I want to implement the column call of the following tree structure:

How to write the background controller, my database is as follows:

Who can help me solve this problem

Answer 1

The simplest idea: query the records with pid 0 in the database and then query the sub-columns in a loop. The number of layers required is just a few loops