asp.net XML改变节点的位置

Question

我正在构建xml文件：

public YandexMarketDoc()
    {
        var root = _doc.CreateElement("yml_catalog");
        root.SetAttribute("date", DateTime.Now.ToString("yyyy-MM-dd HH:mm"));
        _doc.AppendChild(root);

        var shop = _doc.CreateElement("shop");
        root.AppendChild(shop);

        Categories = _doc.CreateElement("categories");
        shop.AppendChild(Categories);

        Items = _doc.CreateElement("offers");
        shop.AppendChild(Items);
    }

比我添加节点到类别节点：

public override void AddCategory(string title, int id, int parent)
    {
        var i = Categories.OwnerDocument.CreateElement("category");
        i.SetAttribute("id", id.ToString());

        if(parent > 0)
            i.SetAttribute("parentId", parent.ToString());

        i.InnerText = title;

        Categories.AppendChild(i);
    }

但是类别节点中的结果节点会更改其位置。这是将节点插入Category：

的方法

static void FillTemplates(PriceList doc, List<PriceAgregator> price)
    {
        foreach (PriceAgregator i in price.Where(r=> r.Level == 0))
        {
            foreach (PriceAgregator level1 in price.Where(r => r.Level == 1 && r.ParentID == i.ID))
            {
                AddCategory(doc, i.Title, level1.ParentID);
                foreach (PriceAgregator pa in price.Where(r => r.Level == 2 && r.ParentID == level1.ID))
                {
                    int p = 0;

                    foreach (PriceAgregatorItem item in pa.Childs)
                    {
                        if (AddItem(doc, item))
                            p++;
                    }

                    if (p == 0)
                    {
                        RemoveCategory(doc, i.ID);
                    }
                    else
                    {
                        AddCategory(doc, pa.Title, pa.ID, level1.ParentID);
                    }
                }
            }
        }
    }

我认为首先插入必须从笔画类别： AddCategory（doc，i.Title，level1.ParentID）;