private function recurse_children($parent, &$options, $depth = 1) {
    $parent->childrens->map(function($child) use (&$options, $depth) {
      $options[$child->id] = str_repeat('-', $depth) .' '. $child->name;

      if ($child->childrens) {
        $this->recurse_children($child, $options, $depth+1);
      }
    });
  }