递归生成树结构 .net 2.0 treeview 控件

//this.getChildTree("137","",this.TreeView1.Nodes[0]);
public void getChildTree(string pid, string classname, TreeNode tns)
{
DataTable dt = DbHelperOleDb.Query("select classid,parentid,classname from [zone] where [parentid]=" + pid).Tables[0];
if (dt.Rows.Count > 0)
{
for (int i = 0; i < dt.Rows.Count; i++)
{
DataTable dts = DbHelperOleDb.Query("select classid,parentid,classname from [zone] where [parentid]=" + Convert.ToString(dt.Rows[i]["classid"] ?? "-100")).Tables[0];
if (dts.Rows.Count > 0)
{
TreeNode tn = new TreeNode();
tn.Text = Convert.ToString(dt.Rows[i]["classname"] ?? "");
tn.Expanded = true;
tns.ChildNodes.Add(tn);

//this.TreeView1.Nodes.Add(tn);
//this.Response.Write(" <li expanded=1><span>" + Convert.ToString(dt.Rows[i]["classname"] ?? "") + "</span><ul>");
this.getChildTree(Convert.ToString(dt.Rows[i]["classid"] ?? ""), Convert.ToString(dt.Rows[i]["classname"] ?? ""), tn);
//Response.Write("</ul></li>");

}
else
{
TreeNode tn = new TreeNode();
tn.Text = Convert.ToString(dt.Rows[i]["classname"] ?? "");
tn.Expanded = true;
tn.NavigateUrl = "main.aspx?classid=" + Convert.ToString(dt.Rows[i]["classid"] ?? "");
tn.Target = "main";
tns.ChildNodes.Add(tn);
// this.TreeView1.Nodes.Add();
// Response.Write("<li><a href=\"main.aspx?classid=" + Convert.ToString(dt.Rows[i]["classid"] ?? "") + "\" target=\"main\">" + Convert.ToString(dt.Rows[i]["classname"] ?? "") + "</a></li>");
}
}
}
else
{
TreeNode tn = new TreeNode();
tn.Text = classname;// Convert.ToString(dt.Rows[i]["classname"] ?? "");
tn.Expanded = true;
tn.NavigateUrl = "main.aspx?classid=" + pid;// Convert.ToString(dt.Rows[i]["classid"] ?? "");
tn.Target = "main";
tns.ChildNodes.Add(tn);
//Response.Write("<li><a href=\"main.aspx?classid=" + pid + "\" target=\"main\">" + classname + "</a></li>");
}

}