easyui树形结构选择

如上图所示，要有如些效果

前台HTML代码

<select id="ShareTo" name="ShareTo" class="easyui-combotree"    data-options="url:'/BlueVacation/Controller/ScheduleHandler.ashx?op=tree'"   multiple ></select>

后台C#的代码

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;
        }