public static function nestedFolderIDs($parentID, $maxDepth = 5)
    {
        $ids = [$parentID];
        if ($maxDepth === 0) {
            return $ids;
        }
        $childIDs = Folder::get()->filter('ParentID', $parentID)->column('ID');
        foreach ($childIDs as $childID) {
            $ids = array_merge($ids, static::nestedFolderIDs($childID, $maxDepth - 1));
        }
        return $ids;
    }