tree.php

public function list_level($arr,$pid=0,$lev=0){
        $data = array();
        foreach($arr as $k=>$v){
            if($v['pid'] == $pid){
                $v['level'] = $lev;
                $data[] = $v;
                $data=array_merge($data,$this->list_level($arr,$v['id'],$lev+1));
            }
        }
        return $data;
    }