这种节点形式我要怎么才能标记才能得到
<upgradeGoods num="2">3ldsjf2dl</upgradeGoods>
现在我是
 public class UpgradeGoods
    {
        /// <summary>
        /// 卖品编码/套餐编码
        /// </summary>
        [XmlAttribute("num")]
        public string ItemNum { get; set; }
        public string GoodsInfoId { get; set; }
    }
得到的结果是
<upgradeGoods num="
<GoodsInfoId>
3ldsjf2dl
</GoodsInfoId>
</upgradeGoods>