public function Tree($arr, $pid = 0, $level = 0){static $list = [];foreach ($arr as $key => $value) {if ($value["pid"] == $pid) {$value["level"] = $level;$list[] = $value;unset($arr[$key]); //删除已经排好的数据为了减少遍历的次数，当然递归本身就很费神就是了$this->Tree($arr, $value["id"], $level + 1);}}return $list;}