refresh tree view after button click

i have used below code for filtering tree view, it seems search function works correctly, but i do not know how to refresh tree view and populate that after clicking the button.

private IEnumerable<TreeNode> FindNodeByValue(TreeNodeCollection nodes, string searchstring)
    {
        foreach (TreeNode node in nodes)
        {
            if (node.Value.IndexOf(searchstring,
                  StringComparison.CurrentCultureIgnoreCase) >= 0)
                yield return node;
            else
            {
                foreach (var subNode in FindNodeByValue(node.ChildNodes, searchstring))
                    yield return subNode;
            }
        }
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
       
        var query= FindNodeByValue(TreeView1.Nodes, fieldFilterTxtBx.Text);
        if (query != null)
        {
            //TreeView1.Nodes[0].Expand();
            //TreeView1.Nodes.Clear();
            foreach (TreeNode node in query.ToList())
            {
                TreeView1.Nodes.Add(node);
                
            }


            //  TreeNode newnode = new TreeNode("Detail Engineering");
            // TreeView1.Nodes.Add(newnode);

            TreeView1.ExpandAll();
        }

        else
        {

            Label1.Text = "No file found";

        }
    }

Tags: LINQ, ASP.NET