private void ProductType_MouseDoubleClick(object sender, MouseButtonEventArgs e)
        {
            EditArticleTypeWindow editArticleTypeWindow = new EditArticleTypeWindow((ProductType)ProductTypeTree.SelectedItem);

            editArticleTypeWindow.ShowDialog();
            updateProductTree();
        }
        private void NewProductType_Click(object sender, RoutedEventArgs e)
        {
            EditArticleTypeWindow editArticleTypeWindow = new EditArticleTypeWindow(null);

            editArticleTypeWindow.ShowDialog();
            updateProductTree();
        }