Array
(
    [0] => Array
        (
            [id] => 1
            [name] => 一级目录A
            [pid] => 0
            [sort] => 1
            [_child] => Array
                (
                    [0] => Array
                        (
                            [id] => 5
                            [name] => 二级目录A-1
                            [pid] => 1
                            [sort] => 1
                        )

                    [1] => Array
                        (
                            [id] => 6
                            [name] => 二级目录A-2
                            [pid] => 1
                            [sort] => 2
                            [_child] => Array
                                (
                                    [0] => Array
                                        (
                                            [id] => 14
                                            [name] => 三级目录A-2-1
                                            [pid] => 6
                                            [sort] => 1
                                        )

                                    [1] => Array
                                        (
                                            [id] => 15
                                            [name] => 三级目录A-2-2
                                            [pid] => 6
                                            [sort] => 2
                                        )

                                )

                        )

                    [2] => Array
                        (
                            [id] => 7
                            [name] => 二级目录A-3
                            [pid] => 1
                            [sort] => 3
                        )

                )

        )

    [1] => Array
        (
            [id] => 2
            [name] => 一级目录B
            [pid] => 0
            [sort] => 2
            [_child] => Array
                (
                    [0] => Array
                        (
                            [id] => 8
                            [name] => 二级目录B-1
                            [pid] => 2
                            [sort] => 1
                        )

                    [1] => Array
                        (
                            [id] => 9
                            [name] => 二级目录B-2
                            [pid] => 2
                            [sort] => 2
                            [_child] => Array
                                (
                                    [0] => Array
                                        (
                                            [id] => 17
                                            [name] => 三级目录B-2-1
                                            [pid] => 9
                                            [sort] => 2
                                        )

                                )

                        )

                    [2] => Array
                        (
                            [id] => 10
                            [name] => 二级目录B-3
                            [pid] => 2
                            [sort] => 3
                        )

                )

        )

    [2] => Array
        (
            [id] => 3
            [name] => 一级目录C
            [pid] => 0
            [sort] => 3
            [_child] => Array
                (
                    [0] => Array
                        (
                            [id] => 11
                            [name] => 二级目录C-1
                            [pid] => 3
                            [sort] => 2
                            [_child] => Array
                                (
                                    [0] => Array
                                        (
                                            [id] => 16
                                            [name] => 三级目录C-1-1
                                            [pid] => 11
                                            [sort] => 1
                                        )

                                )

                        )

                )

        )

    [3] => Array
        (
            [id] => 4
            [name] => 一级目录D
            [pid] => 0
            [sort] => 4
            [_child] => Array
                (
                    [0] => Array
                        (
                            [id] => 12
                            [name] => 二级目录D-1
                            [pid] => 4
                            [sort] => 1
                        )

                    [1] => Array
                        (
                            [id] => 13
                            [name] => 二级目录D-2
                            [pid] => 4
                            [sort] => 2
                        )

                )

        )

)
Array
(
    [0] => 11
    [1] => 3
)