无限级分类中的一个问题 [ 2.0 版本 ]

<?php
$cate = array(
    0 => array('id' => 1, 'pid' => 0, 'name' => '江西省'),
    1 => array('id' => 2, 'pid' => 0, 'name' => '浙江省'),
    2 => array('id' => 3, 'pid' => 1, 'name' => '上饶市'),
    3 => array('id' => 4, 'pid' => 3, 'name' => '广丰县'),
    4 => array('id' => 5, 'pid' => 2, 'name' => '杭州市'),
    5 => array('id' => 6, 'pid' => 5, 'name' => '西湖'),
    6 => array('id' => 7, 'pid' => 6, 'name' => '断桥'),
 );

function getLevel ($cate,$pid,$id,$i =1) {
    foreach ($cate as $v) {
        if ($v['pid'] == $pid) {                    
            if($v['id']==$id){
                return $i;
            }
            getLevel ($cate,$v['id'],$id,$i+1);      
        }
    }
} 

$L=getLevel ($cate,2,5); //等1
$L=getLevel ($cate,2,7); //这里为什么为空？

?>