查找子集，并分类返回

//查找子集 function tree_son($data,$pid){     $son=[];     foreach ( $data as $key=>$vo){         if ($vo['pid']==$pid){             $vo['son']=tree_son($data, $vo['id']);             $son[]=$vo;         }     }     return $son;}

public  function _initialize(){        $menu=Db('access')->select();        $list=[];        foreach ($menu as $key=>$vo){            if ($vo['pid']==0){               $vo['son']=tree_son($menu,$vo['id']);               $list[]=$vo;            }        }        self::assign('menu',$list);    }