We usally wants to male a ul/li tree from an array having parent id within each individual record :

$subjecttopic=Array
(
    [0] => Array
        (
            [id] => 52b28146f484a5a410000029
            [name] => Addtion
            [parent] => 0
            [updated] => 2013-12-23 09:37:43
        )
    [1] => Array
        (
            [id] => 52b28150f484a5a41000002a
            [name] => Subtraction
            [parent] => 0
            [updated] => 2013-12-23 09:37:49
        )
    [2] => Array
        (

            [id] => 52b281c2f484a59c1000002f
            [name] => 2 Digit Simple Addition
            [parent] => 52b28184f484a59c1000002b
            [updated] => 2013-12-23 09:37:26
        )
    [3] => Array
        (

            [id] => 52b281c9f484a59c10000030
            [name] => 3 Digit Simple Addition
            [parent] => 52b28189f484a59c1000002c
            [updated] => 2013-12-23 09:37:58
        )
    [4] => Array
        (

            [id] => 52b281d4f484a59c10000031
            [name] => 3 Digit Carry Addition
            [parent] => 52b28189f484a59c1000002c
            [updated] => 2013-12-23 09:38:06
        )
    [5] => Array
        (

            [id] => 52b281a6f484a59c1000002d
            [name] => 2 Digit Subtraction
            [parent] => 52b28150f484a5a41000002a
            [updated] => 2013-12-23 09:38:16
        )
    [6] => Array
        (

            [id] => 52b28210f484a5cc1000002a
            [name] => 2 Digit Borrow Subtraction
            [parent] => 52b281a6f484a59c1000002d
            [updated] => 2013-12-23 09:38:49
        )
    [7] => Array
        (

            [id] => 52b28218f484a5cc1000002b
            [name] => 3 Digit Borrow Subtraction
            [parent] => 52b281abf484a59c1000002e
            [updated] => 2013-12-23 09:38:54
        )
    [8] => Array
        (

            [id] => 52b281abf484a59c1000002e
            [name] => 3 Digit Subtraction
            [parent] => 52b28150f484a5a41000002a
            [updated] => 2013-12-23 09:38:59
        )
    [9] => Array
        (

            [id] => 52b2821ff484a5cc1000002c
            [name] => 3 Digit Simple Subtraction
            [parent] => 52b281abf484a59c1000002e
            [updated] => 2013-12-23 09:39:04
        )
    [10] => Array
        (

            [id] => 52b28189f484a59c1000002c
            [name] => 3 Digit Addition
            [parent] => 52b28146f484a5a410000029
            [updated] => 2013-12-23 09:40:24
        )
    [11] => Array
        (

            [id] => 52b281dbf484a59c10000032
            [name] => 2 Digit Carry Addition
            [parent] => 52b28184f484a59c1000002b
            [updated] => 2013-12-23 09:40:41
        )
    [12] => Array
        (
            [id] => 52b28184f484a59c1000002b
            [name] => 2 Digit Addition
            [parent] => 52b28146f484a5a410000029
            [updated] => 2013-12-23 09:40:56
        )
    [13] => Array
        (
            [id] => 52b28208f484a5cc10000029
            [name] => 2 Digit Simple Subtraction
            [parent] => 52b281a6f484a59c1000002d
            [updated] => 2013-12-23 09:41:01
        )
)

public function buildTopicTree($rows, $parent = 0) {
        $result = "
";
        foreach ($rows as $row) {
            if ($row['parent'] == $parent) {
                if (count($row['children']) > 0){
                    $result.= "
{$row['name']}";
                    $result.= $this->buildTopicTree($rows,$row[_id]->{'$id'});
                }else{
                    $result.= "
{$row['name']}";
                    $result.= $this->buildTopicTree($rows,$row[_id]->{'$id'});
                }
                    $result.= "
";
            }
        }
        $result.= "
";
        return $result;
}

 $resultstr=$this->buildTopicTree($subjecttopic);