public function getFlatSubItems()
    {
        $key = $this->getKey();
        $itemIds = Arr::get($this->_tree, $key);
        $flatItemIds = $this->_dot($itemIds, $key ? $key . '.' : '');
        $items = [];
        foreach ($flatItemIds as $itemId => $value) {
            $items[$itemId] = $this->_itemData[$itemId];
        }
        return $items;
    }