using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;

/// <summary>
///ResponseHelper 的摘要说明
/// </summary>
public static class ResponseHelper
{
    public static void Redirect(string url, string target, string windowFeatures)
    {
        HttpContext context = HttpContext.Current;
        if ((String.IsNullOrEmpty(target) || target.Equals("_self", StringComparison.OrdinalIgnoreCase)) && String.IsNullOrEmpty(windowFeatures))
        {
            context.Response.Redirect(url);
        }
        else
        {
            Page page = (Page)context.Handler;
            if (page == null)
            {
                throw new InvalidOperationException("Cannot redirect to new window outside Page context.");
            } 
            url = page.ResolveClientUrl(url); 
            string script;
             if (!String.IsNullOrEmpty(windowFeatures))
             { 
                   script = @"<script>window.open(""{0}"", ""{1}"", ""{2}"");</script>"; 
             }
            else
            {
                script = @"<script>window.open(""{0}"", ""{1}"");</script>";
            }
            script = String.Format(script, url, target, windowFeatures);
            page.RegisterStartupScript("", script);
        }
    }
}

------解决方案--------------------

别用selectedNodeChanged事件
treeNode.NavigateUrl="TopicList.aspx?Department=1"
treeNode.Target = "ContentFrame"