带有“全选”的combotree

<div id="setBtn_dd" class="easyui-window" data-options="iconCls:'icon-save',buttons:'#setBtn_dlg-buttons',closed:true,modal:true,width:380,height:380">
        <form id="setBtn_ff" method="post" autocomplete="off" style="margin-top: 30px">
            <table class="tb1">
                <tr hidden="hidden">
                    <td class="td1">MenuID：</td>
                    <td class="td2">
                        <input id="setBtn_MenuID" class="easyui-validatebox textbox" type="text" name="menuId" style="width: 200px; height: 30px;" /></td>
                </tr>
                <tr>
                    <td class="td1">菜单名称：</td>
                    <td class="td2">
                        <input id="setBtn_MenuName" class="easyui-validatebox textbox" type="text" name="menuName" data-options="required:'true',validType:'maxLength[100]'" style="width: 200px; height: 30px;" disabled="disabled" /></td>
                </tr>
                <tr>
                    <td class="td1">按钮：</td>
                    <td class="td2">
                        <select id="combotree_setBtn" class="easyui-combotree" name="combotree_setBtn" data-options="validType:'maxLength[100]',multiple:true" style="width: 200px; height: 30px;" /></td>
                </tr>
            </table>

            <div id="setBtn_dlg-buttons">
                <a id="setBtn_ddok" href="javascript:void(0)" onclick="javascript:saveMenuBtn();" class="easyui-linkbutton" data-options="iconCls:'icon icon-ok'">保存</a>
                <a id="setBtn_ddcancel" href="javascript:void(0)" onclick="javascript:$('#setBtn_dd').window('close');" class="easyui-linkbutton" data-options="iconCls:'icon icon-cancel'">取消</a>
            </div>
        </form>
    </div>

$("#z-toolbar").on("click", "#btnSetMenuButton", function () {
        var row = $('#tbMenu').datagrid('getSelected');
        if (row == null) {
            $.messager.alert('警告', '请选择至少一行数据', 'warning');
            return;
        }

        $.ajax({
            type: 'post',
            dataType: "json",
            url: '/Handlers/MenuHandler.ashx?action=IsExistSon&menuId=' + encodeURI(row.menuId),　　//判断是否有下级
            success: function (data) {
                if (data.Success) {
                    $('#setBtn_dd').dialog({
                        closed: false,
                        title: '分配按钮',
                        onBeforeOpen: function () {
                            //加载时选中已经分配好的按钮
                            $.ajax({
                                type: 'post',
                                dataType: "json",
                                url: '/Handlers/MenuButtonHandler.ashx?action=LoadMenuButton&menuId=' + encodeURI(row.menuId),

                                success: function (mb_data) {
                                    if (mb_data.Success) {
                                        $('#combotree_setBtn').combotree('setValues', mb_data.Message);
                                    }
                                }
                            })
                        }
                    });
　　　　　　　　　　　　//向combotree绑定值
                    $('#combotree_setBtn').combotree(
                        {
                            url: "/Handlers/ButtonHandler.ashx?action=GetButtonTree"
                        });
                    $('#setBtn_ff').form('load', row);
                } else {
                    $.messager.show({
                        title: '错误',
                        msg: data.Message
                    });
                }
            }
        })
    })

 private void GetButtonTree(HttpContext context)
        {
            string where = "1=1";
            List<Model_tb_button> btnList = new BLL_Button().GetButtonTable(where);

            StringBuilder sbStr = new StringBuilder();
            sbStr.Append("[{\"id\":0, \"text\": \"全选\", \"children\":[");
            if (btnList != null && btnList.Count > )
            {
                foreach (var item in btnList)
                {
                    sbStr.Append("{\"id\":" + item.btnId + ", \"text\":\"" + item.btnName + "\", \"iconCls\":\"" + item.btnIcon + "\"},");
                }
                sbStr.Remove(sbStr.Length - , );
            }
            sbStr.Append("]}]");

            Response.WriteJson(context, sbStr);
        }

BLL
public List<Model_tb_button> GetButtonTable(string where)
        {
            DataSet ds = this.dal.GetButtonTable(where);
            return ModelHandler<Model_tb_button>.FillModel(ds.Tables[]);
        }

DLL
public DataSet GetButtonTable(string where)
        {
            StringBuilder sbSql = new StringBuilder();
            sbSql.Append("SELECT btnId AS id, btnName AS text, btnIcon AS iconCls, * FROM dbo.tb_button  ");
            if (!string.IsNullOrEmpty(where))
            {
                sbSql.Append("  WHERE   " + where);
            }  

            return DbHelperSQL.Query(sbSql.ToString());
        }

Model
[Serializable]
    public partial class Model_tb_button
    {
        public Model_tb_button()
        { }
        #region Model
        private int _btnid;
        private string _btnname;
        private string _btncode;
        private string _btnicon;
        private DateTime? _createtime;
        private string _createby;
        private DateTime? _updatetime;
        private string _updateby;
        /// <summary>
        ///
        /// </summary>
        public int btnId
        {
            set { _btnid = value; }
            get { return _btnid; }
        }
        /// <summary>
        ///
        /// </summary>
        public string btnName
        {
            set { _btnname = value; }
            get { return _btnname; }
        }
        /// <summary>
        ///
        /// </summary>
        public string btnCode
        {
            set { _btncode = value; }
            get { return _btncode; }
        }
        /// <summary>
        ///
        /// </summary>
        public string btnIcon
        {
            set { _btnicon = value; }
            get { return _btnicon; }
        }
        /// <summary>
        ///
        /// </summary>
        public DateTime? createTime
        {
            set { _createtime = value; }
            get { return _createtime; }
        }
        /// <summary>
        ///
        /// </summary>
        public string createBy
        {
            set { _createby = value; }
            get { return _createby; }
        }
        /// <summary>
        ///
        /// </summary>
        public DateTime? updateTime
        {
            set { _updatetime = value; }
            get { return _updatetime; }
        }
        /// <summary>
        ///
        /// </summary>
        public string updateBy
        {
            set { _updateby = value; }
            get { return _updateby; }
        }
        #endregion Model

    }