Custom Post Type children and grand-children in one list

So, here is the story: i made a product catalogue with 3 custom post types:

- Product
    - Filegroup (Child of Product)
        - File (Child of Filegroup)

When on product page it should show a list with the Filegroup title and the loose files under the correct Filegroup. But it shows the children at both parents

It’s like this now:

- Filegroup 1
    - File 3 (child of Filegroup 2)
    - File 1 (child of Filegroup 1)
    - File 2 (child of Filegroup 1)

- Filegroup 2
    - File 3 (child of Filegroup 2)
    - File 1 (child of Filegroup 1)
    - File 2 (child of Filegroup 1)

And it needs to be:

- Filegroup 1
    - File 1 (child of Filegroup 1)
    - File 2 (child of Filegroup 1)

- Filegroup 2
    - File 3 (child of Filegroup 2)

My current script

<?php
    $childargs = array(
    'post_type' => 'filegroup',
    'numberposts' => -1,
    'order' => 'ASC',
    );
    $child_posts = get_posts($childargs);

    foreach ($child_posts as $child_post){
    $parentid = $child_post->ID;
        ?>
            <ul>
                <li><strong><?php echo $child_post->post_title; ?></strong></li>
                    <?php
                        $childargs2 = array(
                        'post_type' => 'file',
                        'numberposts' => -1,
                        'post_parent' => '0'
                        );
                        $child_posts2 = get_posts($childargs2);

                        foreach ($child_posts2 as $child_post){
                        ?>
                            <li><?php echo $child_post->post_title; ?></li>
                        <?php
                        }
                    ?>
            </ul>

        <?php
    }
?>