求大神一个递归无限级方法代码，真心谢谢

<?php
$arr=['lin',
'wang',
'zhang',
['lin1',
'wang1',
'zhang1',
['lin2',
'wang2',
'zhang2'
],
],
];
function maxforeach($array){
foreach ($array as $value){
if(is_array($value)){
maxforeach($value);
}else{
echo $value.'<br>';
}
}
}
maxforeach($arr);

public function list_product_attr($pid=0){
$DbAttr = D("attr");
$cates = $DbAttr->order('id desc')->select();
return $this->_tree($cates,$pid);
}
private function _tree($arr,$pid=0,$level=0){
//保存重组的结果，用静态变量；
static $tree=array();
foreach ($arr as $v){
if($v['pid']==$pid){
$v['level']=$level;
$tree[]=$v;
$this->_tree($arr,$v['id'],$level+1);
}
}
return $tree;
}
public function index(){
$data=$this->list_attr();
$this->assign($data);
$this->display();
}