Something like this should do the trick:
XmlDocument xmlDoc = new XmlDocument();
serializer.Serialize(ms, obj);
ms.Position = 0;
xmlDoc.Load(ms);
XmlElement newElem = xmlDoc.CreateElement("Response");
//wrong: works for only 1 child element
//kept for edit/reference
//foreach (XmlNode item in xmlDoc.DocumentElement.ChildNodes)
//{
// newElem.AppendChild(item);
//}
while (xmlDoc.DocumentElement.ChildNodes.Count != 0)
{
newElem.AppendChild(xmlDoc.DocumentElement.ChildNodes[0]);
}
xmlDoc.DocumentElement.AppendChild(newElem);
EDIT replaced the foreach
loop with a correct and general implementation using a while
loop.