treeview loses data when page is being refreshed in asp.net

Question

Hi,

I have a treeview and I written a code for his "treeNodePopulate" event:

protected void ycActiveTree_TreeNodePopulate(object sender, TreeNodeEventArgs e)
    {
        if (Application["idList"] != null && e.Node.Depth == 0)
        {
            string[] words = ((String)Application["idList"]).Split(' '); // Yellow Card details
            TreeNode child = new TreeNode("");
            // Go over all the yellow card details and populate the treeview
            for (int i = 1; i < words.Length; i++)
            {
                child.SelectAction = TreeNodeSelectAction.None;
                // Same yellow card
                if (words[i] != "*")
                {
                    // End of details and start of point ip's 
                    if (words[i] == "$")
                    {
                        // Add the yellow card node
                        TreeNode yellowCardNode = new TreeNode(child.Text);
                        yellowCardNode.SelectAction = TreeNodeSelectAction.Expand;
                        e.Node.ChildNodes.Add(yellowCardNode);
                        child.Text = "";
                    }
                    // yellow card details
                    else
                    {
                        child.Text = child.Text + words[i] + " ";
                    }
                }
                // End of yellow card
                else
                {
                    child.PopulateOnDemand = false;
                    child.SelectAction = TreeNodeSelectAction.None;

                    // Populate the yellow card node
                    e.Node.ChildNodes[e.Node.ChildNodes.Count - 1].ChildNodes.Add(child);

                    TreeNode moveChild = new TreeNode("Move To Reviewed");
                    moveChild.PopulateOnDemand = false;
                    moveChild.SelectAction = TreeNodeSelectAction.Select;

                    e.Node.ChildNodes[e.Node.ChildNodes.Count - 1].ChildNodes.Add(moveChild);
                    child = new TreeNode("");
                }
            }
            Application["idList"] = null;
        }
    }

I want the treenode to get the data from the Application variable and then nullify the Application variable so that the tree will take data from Applcation only if there is something in it (I put data into the application from another page and then redirect to this page) But when I refresh this page the data in the treenode isnt being saved. I mean after the refresh the Application is null so he isnt doing anything. The question is why is the data that I put in the treenode earlier isnt being saved? The "enableViewState" property is set to "true"..

Thanks in advance,

Greg