树形结构 查找上下级

<?php
array (
1 =>array (
'cat_id' => '1',
'cat_name' => '手机类型',
'parent_id' => '0',
'child' =>array (
2 => array (
'cat_id' => '2',
'cat_name' => 'CDMA手机',
'parent_id' => '1',
),
3 => array (
'cat_id' => '3',
'cat_name' => 'GSM手机',
'parent_id' => '1',
),
4 => array (
'cat_id' => '4',
'cat_name' => '3G手机',
'parent_id' => '1',
),
5 => array (
'cat_id' => '5',
'cat_name' => '双模手机',
'parent_id' => '1',
),
),
),
6 => array (
'cat_id' => '6',
'cat_name' => '手机配件',
'parent_id' => '0',
'child' => array (
7 => array (
'cat_id' => '7',
'cat_name' => '充电器',
'parent_id' => '6',
),
8 => array (
'cat_id' => '8',
'cat_name' => '耳机',
'parent_id' => '6',
),
9 => array (
'cat_id' => '9',
'cat_name' => '电池',
'parent_id' => '6',
'child' => array(
101=>array (
'cat_id' => '101',
'cat_name' => '充电器101',
'parent_id' => '9',
),
102=>array (
'cat_id' => '102',
'cat_name' => '充电器102',
'parent_id' => '9',
),
103=>array (
'cat_id' => '103',
'cat_name' => '充电器103',
'parent_id' => '9',
),
),
),
11 => array (
'cat_id' => '11',
'cat_name' => '读卡器和内存卡',
'parent_id' => '6',
),
),
),
12 => array (
'cat_id' => '12',
'cat_name' => '充值卡',
'parent_id' => '0',
'child' =>  array (
13 => array (
'cat_id' => '13',
'cat_name' => '小灵通/固话充值卡',
'parent_id' => '12',
),
14 => array (
'cat_id' => '14',
'cat_name' => '移动手机充值卡',
'parent_id' => '12',
),
15 => array (
'cat_id' => '15',
'cat_name' => '联通手机充值卡',
'parent_id' => '12',
),
),
),
);