get the value of selected node in the treeview

protected void Page_Load(object sender, EventArgs e)
      {

if (Page.IsPostBack == false)
            {
                DirectoryInfo RootDir = new DirectoryInfo(Server.MapPath("~/AudioFiles"));

                // output the directory into a node
                TreeNode RootNode = OutputDirectory(RootDir, null);

                // add the output to the tree
                TreeView1.Nodes.Add(RootNode);
            }

        }
 TreeNode OutputDirectory(DirectoryInfo directory, TreeNode parentNode)
    {
        // validate param
        if (directory == null) 
            return null; 

        // create a node for this directory
        TreeNode DirNode = new TreeNode(directory.Name);

        // get subdirectories of the current directory
        DirectoryInfo[] SubDirectories = directory.GetDirectories();

        // OutputDirectory(SubDirectories[0], "Directories");
        // output each subdirectory
        for (int DirectoryCount = 0; DirectoryCount < SubDirectories.Length; DirectoryCount++)
        {
            OutputDirectory(SubDirectories[DirectoryCount], DirNode);
        }

        // output the current directories file
        FileInfo[] Files = directory.GetFiles();
        for (int FileCount = 0; FileCount < Files.Length; FileCount++)
        {
            DirNode.ChildNodes.Add(new TreeNode(Files[FileCount].Name));
        }
       
        // if the parent node is null, return this node
        // otherwise add this node to the parent and return the parent
        if (parentNode == null)
        {
            return DirNode;
        }
        else
        {
            parentNode.ChildNodes.Add(DirNode);
            return parentNode;
        }
    }