private void CategoryTree_Expanded(object sender, RoutedEventArgs e)
        {
            TreeViewItem this_TreeViewItem        = e.Source as TreeViewItem;
            TypeDigest   parentCategoryTypeDigest = (TypeDigest)this_TreeViewItem.Tag;

            if (this_TreeViewItem.Items.Count > 0 && this_TreeViewItem.Items[0] is TreeViewItem && ((TreeViewItem)this_TreeViewItem.Items[0]).Tag is LoadingTreeViewItem)
            {
                this_TreeViewItem.Items.Clear();
                foreach (TypeDigest childTypeDigest in _typeRepository.GetTypeDigestsByParent(parentCategoryTypeDigest.Id))
                {
                    this_TreeViewItem.Items.Add(CreateCategoryTreeViewItem(childTypeDigest.Code, childTypeDigest));
                }
            }
        }