Thinkphp5 controllers tree classification

Public function getrtree(){
       
        $data[]=array('id'=>1,'pid'=>0,'name'=>'中国');
        $data[]=array('id'=>2,'pid'=>0,'name'=>'美国');
        $data[]=array('id'=>3,'pid'=>0,'name'=>'韩国');
        $data[]=array('id'=>4,'pid'=>1,'name'=>'北京');
        $data[]=array('id'=>5,'pid'=>1,'name'=>'上海');
        $data[]=array('id'=>6,'pid'=>1,'name'=>'广西');
        $data[]=array( 'id' => 7, 'pid' => 6, 'name' => ' Guilin' );
         $ Data [] = Array ( 'ID' =>. 8, 'PID' =>. 6, 'name' = > 'Nanning' );
         $ Data [] = Array ( 'ID' =>. 9, 'PID' =>. 6, 'name' => 'Liuzhou' );
         $ Data [] = Array ( 'ID' => 10 , 'pid' => 2, 'name' => ' New York' );
         $ Data [] = Array ( 'ID' =>. 11, 'pid' => 2, 'name' => ' Washington' );
         $ Data [] = Array ( 'ID' => 12 is, 'PID' =>. 3, 'name' => 'Seoul');
       
        $tree=$this->build_tree($data,0);
        print_r($tree);
        print(json_encode($tree,true));
       
    }


    function findChild(&$arr,$id){
        $childs=array();
        foreach ($arr as $k => $v){
            if($v['pid']== $id){
                $childs[]=$v;
            }
        }
        return $childs;
    }
   
    function build_tree($rows,$root_id){
        $childs=$this->findChild($rows,$root_id);
        if(empty($childs)){
            return null;
        }
        foreach ($childs as $k => $v){
            $rescurTree=$this->build_tree($rows,$v['id']);
            if( null != $rescurTree){
                $childs[$k]['childs']=$rescurTree;
            }
        }
        return $childs;
    }