DisappearAfter="-1"

 protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            userDatas = Session["User_datas"] as User_Datas;
 
            if (userDatas == null)
            {
                return;
                //ERRORPAGE LOAD!
            }
           create_tree();            
        }
    }

    private void create_tree()
    {
        TreeNode tmp_node;
        TreeNode tmp_Master_Node;
 
        tmp_Master_Node = new TreeNode("test1", "bla");
        tmp_Master_Node.NavigateUrl = "../allgemein.aspx";
        TreeView1.Nodes.Add(tmp_Master_Node);
 
        tmp_node = new TreeNode("c_test1", "bla");
        tmp_node.NavigateUrl = "../Benutzerinformationen.aspx";
        tmp_node.PopulateOnDemand = true;
        tmp_Master_Node.ChildNodes.Add(tmp_node);
 
        tmp_Master_Node = new TreeNode("test2", "bla");
        tmp_Master_Node.NavigateUrl = "../allgemein.aspx";
        TreeView1.Nodes.Add(tmp_Master_Node);
 
        tmp_node = new TreeNode("c_test2", "bla");
        tmp_node.NavigateUrl = "../Benutzerinformationen.aspx";
        tmp_node.PopulateOnDemand = true;
        tmp_Master_Node.ChildNodes.Add(tmp_node);
 
        tmp_node = new TreeNode("c_test3", "bla");
        tmp_node.NavigateUrl = "../Benutzerinformationen.aspx";
        tmp_node.PopulateOnDemand = true;
        tmp_Master_Node.ChildNodes.Add(tmp_node);
 
 
    }