怎么样通过PHP递归遍历多维数组实现无限分类？

<?php
  //$data[]=array('id'=>1,'parentid'=>0,'name'=>'中国','img'=>'52091199');
  $data[]=array('id'=>1,'parentid'=>0,'name'=>'中国');
  $data[]=array('id'=>2,'parentid'=>0,'name'=>'美国');
  $data[]=array('id'=>3,'parentid'=>0,'name'=>'韩国');
  $data[]=array('id'=>4,'parentid'=>1,'name'=>'北京');
  $data[]=array('id'=>5,'parentid'=>1,'name'=>'上海');
  $data[]=array('id'=>6,'parentid'=>1,'name'=>'广西');
  $data[]=array('id'=>7,'parentid'=>6,'name'=>'桂林');
  $data[]=array('id'=>8,'parentid'=>6,'name'=>'南宁');
  $data[]=array('id'=>9,'parentid'=>6,'name'=>'柳州');
  $data[]=array('id'=>10,'parentid'=>2,'name'=>'纽约');
  $data[]=array('id'=>11,'parentid'=>2,'name'=>'华盛顿');
  $data[]=array('id'=>12,'parentid'=>3,'name'=>'首尔');
  $tree=build_tree($data,0);
  //echo memory_get_usage();
  print_r($tree);
 function findChild(&$arr,$id){
 $childs=array();
 foreach ($arr as $k => $v){
  if($v['parentid']== $id){
  $childs[]=$v;
  }
 }
 return $childs;
 }
 function build_tree($rows,$root_id){
 $childs=findChild($rows,$root_id);
 if(empty($childs)){
  return null;
 }
 foreach ($childs as $k => $v){
 $rescurTree=build_tree($rows,$v['id']);
 if( null != $rescurTree){
 $childs[$k]['childs']=$rescurTree;
 }
 }
 return $childs;
 }
?>

Array
(
 [0] => Array
 (
  [id] => 1
  [parentid] => 0
  [name] => 中国
  [childs] => Array
  (
   [0] => Array
   (
    [id] => 4
    [parentid] => 1
    [name] => 北京
   )
   [1] => Array
   (
    [id] => 5
    [parentid] => 1
    [name] => 上海
   )
   [2] => Array
   (
    [id] => 6
    [parentid] => 1
    [name] => 广西
    [childs] => Array
    (
     [0] => Array
     (
      [id] => 7
      [parentid] => 6
      [name] => 桂林
     )
     [1] => Array
     (
      [id] => 8
      [parentid] => 6
      [name] => 南宁
     )
     [2] => Array
     (
      [id] => 9
      [parentid] => 6
      [name] => 柳州
     )
    )
   )
  )
 )
 [1] => Array
 (
  [id] => 2
  [parentid] => 0
  [name] => 美国
  [childs] => Array
  (
   [0] => Array
   (
    [id] => 10
    [parentid] => 2
    [name] => 纽约
   )
   [1] => Array
   (
    [id] => 11
    [parentid] => 2
    [name] => 华盛顿
   )
  )
 )
 [2] => Array
 (
  [id] => 3
  [parentid] => 0
  [name] => 韩国
  [childs] => Array
  (
   [0] => Array
   (
    [id] => 12
    [parentid] => 3
    [name] => 首尔
   )
  )
 )
)