private const string ROOT_FOLDER = \"~/test/\";
public static void AddNodes(FlyTreeNodeCollection nodes, string directoryPath, System.Web.UI.Page page)
{
    string physicalRoot = page.Server.MapPath(ROOT_FOLDER);
    DirectoryInfo directory = new DirectoryInfo(Path.Combine(physicalRoot, directoryPath));
    if (!directory.Exists) return;
    DirectoryInfo[] subDirectories = directory.GetDirectories();
    foreach (DirectoryInfo subDir in subDirectories)
    {
        FlyTreeNode ftn = new FlyTreeNode();
        ftn.Text = HttpUtility.HtmlEncode(subDir.Name);
        ftn.Value = subDir.Name;
        nodes.Add(ftn);
        try
        {
            // do not set populate on demand for nodes that have no nested directories
            ftn.PopulateNodesOnDemand = subDir.GetDirectories().Length > 0;
        }
        catch (Exception ex)
        {
            // add a child node that shows that there was an exception trying to get its child nodes
            AddExceptionNode(ftn.ChildNodes, ex);
        }

    }

    FileInfo[] files = directory.GetFiles();
    foreach (FileInfo file in files)
    {
        FlyTreeNode ftn = new FlyTreeNode();
        ftn.Text = HttpUtility.HtmlEncode(file.Name);
        ftn.Value = file.Name;
        ftn.NavigateUrl = page.ResolveUrl(ROOT_FOLDER + directoryPath + \"/\" + file.Name).Replace(\"//\",\"/\");

        nodes.Add(ftn);
    }
}