ASP.NET

<frameset rows="8%,*">
    <frame src="Header.aspx" />
    <frameset cols="20%,*">
        <frame name="TreeView" src="TreeViewMenu.aspx" />
        <frameset rows="36%,*">
            <frame name="Parameters" src="ErrorPage.aspx" />
            <frame name="DataDisplay" src="DataDisplay.aspx" />
        </frameset>
    </frameset>
</frameset>

public partial class TreeViewMenu : System.Web.UI.Page
{
 
    private const string cFrameName = "Parameters";
    private const string cErrorPage = "ErrorPage.aspx";

    protected void Page_Load(object sender, EventArgs e)
    {
        this.SaveTreeViewState();

        NodeHelper.BuildTreeView(this.TreeView1);

        this.RestoreTreeViewState();
    }

    protected void TreeView1_SelectedNodeChanged(object sender, EventArgs e)
    {
        this.SaveTreeViewState();

        string strSelected = ((TreeView)sender).SelectedNode.Value.ToString();
        string strNavigateURL = ((TreeView)sender).SelectedNode.ToolTip.ToString();

        if (strNavigateURL.Length > 0)
        {
            Response.Write("<script>window.open('" + strNavigateURL + "','" + cFrameName + "');</script>");
        }
        else
        {
            Response.Write("<script>window.open('" + cErrorPage + "','" + cFrameName + "');</script>");
        }
    }
   
    #region Private Procedures

    private void SaveTreeViewState()
    {
        if (IsPostBack)
        {
            List<string> ExpandedList = new List<string>();
            NodeHelper.SaveTreeViewState(TreeView1.Nodes, ExpandedList);
            Session["TreeViewState"] = ExpandedList;
        }
    }

    private void RestoreTreeViewState()
    {
        if (IsPostBack)
        {
            List<string> ExpandedList = (List<string>)Session["TreeViewState"];
            NodeHelper.RestoreTreeViewState(TreeView1.Nodes, ExpandedList);
        }
    }

    #endregion
 
}