easyui树形结构选择

string GetDepaOfUsersTree()
        {
            string json = null;
            if (HttpContext.Current.Cache["userTree"] != null)
            {
                json = HttpContext.Current.Cache["userTree"].ToString();
            }
            else
            {
                var list = DepartmentBll.Instance.GetDepaOfUsersTree();
               json = JsonConvert.SerializeObject(list);
               HttpContext.Current.Cache["userTree"] = json;
            }
         
           
           return json;
        }