private void treeView1_DragDrop(object sender, DragEventArgs e)
 {
   string[] files = (string[])e.Data.GetData(DataFormats.FileDrop);
   if (Directory.Exists(files[0]))
   {
     AddFolder2Group dlg = new AddFolder2Group(Package, SelectedGroup, files[0]);
     if (dlg.ShowDialog() == DialogResult.OK)
     {
       treeView1.Nodes.Clear();
       PopulateTreeView();
       return;
     }
   }
   if (files.Length > 0)
     AddFiles(files);
 }
 private void mnu_add_folder_Click(object sender, EventArgs e)
 {
   TreeNode selectedNode = GetSelectedGroupNode();
   if (selectedNode == null)
   {
     MessageBox.Show("No node selected !");
     return;
   }
   AddFolder2Group dlg = new AddFolder2Group(Package, SelectedGroup);
   if (dlg.ShowDialog() == DialogResult.OK)
   {
     treeView1.Nodes.Clear();
     PopulateTreeView();
   }
 }