treeview 页面不刷新问题

Question

实现：当treeview的节点有子节点时 点击父级节点的文字时 展开其子节点 我现在点击父级节点文字时 是展开子节点了 但是treeview整个刷新了 我想让点击父级节点文字展开子节点的效果和点击父级节点前面的+效果一样不刷新页面这是treeview事件
       /// <summary>
        /// treeview事件
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void TreeViewSpecialized_SelectedNodeChanged(object sender, EventArgs e)
        {
            if (TreeViewSpecialized.SelectedNode.ChildNodes.Count > 0)
            {
                if (TreeViewSpecialized.SelectedNode.Expanded == null || !TreeViewSpecialized.SelectedNode.Expanded.Value)
                {
                    TreeViewSpecialized.SelectedNode.Expand();
                }
                else
                {
                    TreeViewSpecialized.SelectedNode.Collapse();
                }
            }
我的整个页面是用iframe 头部 左部 右部 左部是treeview  右部是点击左部treeview节点的链接出现的相应内容