总结，简单的树结构递归。

        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                DataTable dds= new DataTable(); //id,Title
                creattree(Treeview1.Nodes, dds);
            }
        }
        public void creattree(TreeNodeCollection tnc, DataTable dt)
        {
            TreeNode tn;
            if (dt.Rows.Count > 0) //如果有数据
            {
                for (int i = 0; i < dt.Rows.Count; i++) //遍历数据
                {
                    tn = new TreeNode(); //实例化Tn
                    tn.Text = dt.Rows[i]["colname"].ToString();//Tree显示的文本
                    tn.Value = dt.Rows[i]["id"].ToString();   //Tree的值
                    tn.SelectAction = TreeNodeSelectAction.Expand; //点击触发的事件
                    tnc.Add(tn); //添加子栏目
                    DataTable dts = new DataTable(); //判断（获取上面的id）
                    if (dts.Rows.Count > 0) //如果有子id
                    {
                            creattree(tn.ChildNodes, dts);//执行Creattree
                    }
                }
            }
        }