php递归循环地区

$mylist = array(
    array( 'area_parent_id'=>0,'id'=>1,'area_name' => '河北',),
    array( 'area_parent_id'=>0,'id'=>2,'area_name' => '山东',),
    array( 'area_parent_id'=>0,'id'=>3,'area_name' => '辽宁',),
    array( 'area_parent_id'=>2,'id'=>4,'area_name' => '济南',),
    array( 'area_parent_id'=>2,'id'=>5,'area_name' => '德州',),
    array( 'area_parent_id'=>3,'id'=>6,'area_name' => '沈阳',),
    array( 'area_parent_id'=>3,'id'=>7,'area_name' => '大连',),
    array( 'area_parent_id'=>4,'id'=>8,'area_name' => '济南县1',),
    array( 'area_parent_id'=>5,'id'=>9,'area_name' => '德州县1',),
    array( 'area_parent_id'=>5,'id'=>10,'area_name' => '德州县2',)
);

$arr = array (
        1 => array ( 'area_name' => '河北', 'area_parent_id' => '0', ),
        2 => array ( 'area_name' => '山东', 'area_parent_id' => '0', ),
        3 => array ( 'area_name' => '石家庄','area_parent_id' => '1',),
        4 => array ( 'area_name' => '唐山','area_parent_id' => '1'),
        5 => array ( 'area_name' => '济南','area_parent_id' => '2'),
        6 => array ( 'area_name' => '青岛','area_parent_id' => '2'),
);

function moreList($arr, $p_id){    //数据层级化，
    $r = array();
    foreach($arr as $key=>$val){
        if($val['area_parent_id'] == $p_id) {
            $length = count($r);//0
            $r[$length] = $val;
                
            if($t = moreList($arr,$val['id'])){//$key
                $r[$length]['children'] = $t;
            }
                
        }
    }
    return $r;
}
echo '<pre>';
print_r(moreList($mylist,0));//$arr

echo '</pre>';