public function anAncestorIsMissing($item)
    {
        $parentColumn = $this->parentColumn;
        if (!$item->$parentColumn) {
            return false;
        }
        if (!$this->has($item->$parentColumn)) {
            return true;
        }
        $parent = $this[$item->$parentColumn];

        return $this->anAncestorIsMissing($parent);
    }