php array recursive method

$items = array(
1 => array('id' => 1, 'pid' => 0, 'name' => 'Jiangxi Province'),
2 => array('id ' => 2, 'pid' => 0, 'name' => 'Heilongjiang Province'),
3 => array('id' => 3, 'pid' => 1, ' name' => 'Nanchang City'),
4 => array('id' => 4, 'pid' => 2, 'name' => 'Harbin City'),
5 => ; array('id' => 5, 'pid' => 2, 'name' => 'Jixi City'),
6 => array('id' => 6, 'pid' = > 4, 'name' => 'Xiangfang District'),
7 => array('id' => 7, 'pid' => 4, 'name' => 'Nangang District' ),
8 => array('id' => 8, 'pid' => 6, 'name' => 'Hexing Road'),
9 => array('id' => ; 9, 'pid' => 7, 'name' => 'Xidazhi Street'),
10 => array('id' => 10, 'pid' => 8, 'name ' => 'Northeast Forestry University'),
11 => array('id' => 11, 'pid' => 9, 'name' => 'Harbin Institute of Technology'),
12 = > array('id' => 12, 'pid' => 8, 'name' => 'Harbin Normal University'),
13 => array('id' => 13, 'pid ' => 1, 'name' => 'Ganzhou City'),
14 => array('id' => 14, 'pid' => 13, 'name' => 'Gan County '),
15 => array('id' => 15, 'pid' => 13, 'name' => 'Yudu County'),
16 => array('id' = > 16, 'pid' => 14, 'name' => 'Maodian Town'),
17 => array('id' => 17, 'pid' => 14, 'name ' => 'Datian Township'),
18 => array('id' => 18, 'pid' => 16, 'name' => 'Yiyuan Village'),
19 => ; array('id' => 19, 'pid' => 16, 'name' => 'Shangba Village'),
);

Method 1;
function genTree5($items) {
foreach ($items as $item)
        $items[$item['pid']]['son'][$item['id']] = &$items[$item['id']];          return isset ($items[0]['son']) ? $items[0]['son'] : array();
}

Method 2:
function findChild($arr,$id){
$childs= array();
foreach ($arr as $k => $v){
if($v['pid']== $id){
$childs[]=$v;
}
}
/ / echo "

";print_r($childs);die(); 
 return $childs; 
} 

function build_tree($root_id){ 
 global $items; 
 $childs =array(); 
 $ childrens=findChild($items,$root_id); 
// print_r($childs); 
// die(); 
 if(empty($childs)){ 
 return null; 
 } 
 foreach ($childs as $ k => $v){ 
                                                                                                               using using  -                                                                                         k => } 
 } 
 return $childs; 
}