如何在一个XML中插入序列化的类

using (var ms = new MemoryStream()){    ClassA tryXml = new ClassA {Key = "A", Value = "1"};    XmlSerializer serializer = new XmlSerializer(typeof (ClassA));    serializer.Serialize(ms, tryXml);    var xmlClass = new XmlDocument();    xmlClass.LoadXml(Encoding.UTF8.GetString(ms.ToArray()));    var xmlDocument = new XmlDocument();    xmlDocument.Load("C:\\temp\\TryXml.xml");    XmlElement element = xmlDocument.CreateElement("ClassA");    element.InnerXml = xmlClass.DocumentElement.InnerXml;    xmlDocument.SelectSingleNode("/configuration").AppendChild(element);    xmlDocument.Save("C:\\temp\\TryXml.xml");}