PHP将多维对象格式化为“带深度的选择下拉菜单”

如何将以下内容作为一个漂亮的格式化选择下拉列表进行响应，包括每个级别的"--"？

Array
(
    [0] => stdClass Object
        (
            [id] => 2
            [user_id] => 6
            [title] => First Category
            [parent_id] => 0
        )
    [1] => stdClass Object
        (
            [id] => 4
            [user_id] => 6
            [title] => HTML Times
            [parent_id] => 0
        )
    [2] => stdClass Object
        (
            [id] => 5
            [user_id] => 6
            [title] => Email Ninja
            [parent_id] => 0
        )
    [3] => stdClass Object
        (
            [id] => 6
            [user_id] => 6
            [title] => Taco Night
            [parent_id] => 0
        )
    [4] => stdClass Object
        (
            [id] => 7
            [user_id] => 6
            [title] => SSH
            [parent_id] => 0
            [childs] => Array
                (
                    [0] => stdClass Object
                        (
                            [id] => 10
                            [user_id] => 6
                            [title] => Root Commands
                            [parent_id] => 7
                        )
                    [1] => stdClass Object
                        (
                            [id] => 11
                            [user_id] => 6
                            [title] => Shell
                            [parent_id] => 7
                        )
                    [2] => stdClass Object
                        (
                            [id] => 12
                            [user_id] => 6
                            [title] => Linux
                            [parent_id] => 7
                        )
                    [3] => stdClass Object
                        (
                            [id] => 13
                            [user_id] => 6
                            [title] => Windows
                            [parent_id] => 7
                        )
                )
        )
    [5] => stdClass Object
        (
            [id] => 8
            [user_id] => 6
            [title] => Dinner Tonight
            [parent_id] => 0
            [childs] => Array
                (
                    [0] => stdClass Object
                        (
                            [id] => 9
                            [user_id] => 6
                            [title] => Mexican
                            [parent_id] => 8
                            [childs] => Array
                                (
                                    [0] => stdClass Object
                                        (
                                            [id] => 14
                                            [user_id] => 6
                                            [title] => Tacos
                                            [parent_id] => 9
                                        )
                                )
                        )
                )
        )
)

我知道这个话题涵盖得很广，但对我来说并没有什么意义。经过两天的阅读。。。和阅读。。。和阅读。。。我终于能够从我的数据库中获取这些数据了。现在，我似乎无法让它比第一类更深入地反映出来。

感谢您的帮助和耐心。

以下是我目前如何找到父母：

$level=0；

$categories=$this->mycrate->build_categories（）；

    echo '<select class="input-block-level">';
    function RecursiveWrite($categories) {
        foreach ($categories as $category) {
            echo '<option value="'.$category->id.'">'.$category->title.'</option>';
            RecursiveWrite($category->parent_id);
        }
    }
    RecursiveWrite($categories);
    echo '</select>';