private void btnAddRoot_Click(object sender, EventArgs e)
        {
            CreateCategoryForm dlg = new CreateCategoryForm();

            if (dlg.ShowDialog() == DialogResult.OK)
            {
                _ce.AddRootCategory(tvCategory, dlg.CategoryName);
                tvCategory.Focus();
            }
            //
        }
 private void btnAdd_Click(object sender, EventArgs e)
 {
     if (tvCategory.SelectedNode != null)
     {
         CreateCategoryForm dlg = new CreateCategoryForm();
         if (dlg.ShowDialog() == DialogResult.OK)
         {
             _ce.AddNode(tvCategory.SelectedNode, dlg.CategoryName);
             tvCategory.Focus();
         }
     }
 }