private void directoryMenu_Click(object sender, EventArgs e)
        {
            tree.ShowNodeToolTips = true;
            showDir (tree.Nodes, "c:\\", 2);
        }
 
        private void showDir (TreeNodeCollection target, string path, int levels)
        {
            try
            {
                DirectoryInfo info = new DirectoryInfo (path);
                TreeNode branch = new TreeNode();
                branch.Text = info.Name;
                branch.ToolTipText = path;
                branch.Tag = path;
                target.Add (branch);
 
                if (levels > 1)
                {
                   // using System.IO;
                   DirectoryInfo[] dirs = info.GetDirectories();
                   foreach (DirectoryInfo subdir in dirs)
                       showDir (branch.Nodes, subdir.FullName, levels - 1);
                }
            }
            catch (Exception e)
            {
            }
        }
 
        private void tree_BeforeExpand(object sender, TreeViewCancelEventArgs e)
        {
            if (e.Node.Nodes.Count == 0)
            {
                string path = (string)e.Node.Tag;
                try
                {
                    DirectoryInfo info = new DirectoryInfo(path);
                    DirectoryInfo[] dirs = info.GetDirectories();
                    foreach (DirectoryInfo subdir in dirs)
                        showDir(e.Node.Nodes, subdir.FullName, 2);
                }
                catch (Exception ex)
                {
                }
            }
            else 
            {
                foreach (TreeNode t in e.Node.Nodes)
                try
                {
                    string path = (string) t.Tag;
                    DirectoryInfo info = new DirectoryInfo(path);
                    DirectoryInfo[] dirs = info.GetDirectories();
                    foreach (DirectoryInfo subdir in dirs)
                        showDir(t.Nodes, subdir.FullName, 1);
                }
                catch (Exception ex)
                {
                }
            }
        }