php 递归无线级别分类

<meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
<?php 
$tree=array(
    array('id'=>1,'name'=>'安徽','pid'=>'0'),
    array('id'=>2,'name'=>'北京','pid'=>'0'),
    array('id'=>3,'name'=>'山东','pid'=>'0'),
    array('id'=>4,'name'=>'昭阳区','pid'=>'2'),
    array('id'=>5,'name'=>'合肥市','pid'=>'1'),
    array('id'=>6,'name'=>'蜀山区','pid'=>'5'),
    array('id'=>7,'name'=>'烟台市','pid'=>'3'),
    );
/**
 * @param $data array
 * @param $pid parent_id
 * @param $level
 * @author tian
 */
function tree($data,$pid=0,$level=1){
    static $arr=array();
    foreach($data as $v){
        if($v['pid']==$pid){
            $v['level']=$level;
            $arr[]=$v;
            tree($data,$v['id'],$level+1);
        }
    }
return $arr;
}

$list=tree($tree,0,1);
var_dump($list);
 ?>