adding duplicate element inside an xml file

I have this xmlfile :

<root>
  <Friend_2>
<MESSAGE_BODY>hi</MESSAGE_BODY>
<MESSAGE_SENDER_ID>1</MESSAGE_SENDER_ID>
<MESSAGE_RECEIVER_ID>2</MESSAGE_RECEIVER_ID>
<MESSAGE_CREATION_DATE>2014-08-29T15:33:18.1191004+03:00</MESSAGE_CREATION_DATE>
</Friend_2>
</root>

i am using this function to add elements to this file by doing this :

 private void createNode(string body, string senderid, string receiverid,DateTime creationDate,string path1,string path2)
    {
        XDocument doc1 = XDocument.Load(path1);
        XDocument doc2 = XDocument.Load(path2);
        XElement root1 = new XElement("Friend_"+receiverid);
        XElement root2 = new XElement("Friend_"+senderid);

        root1.Add(new XElement("MESSAGE_BODY", body));
        root1.Add(new XElement("MESSAGE_SENDER_ID", senderid));
        root1.Add(new XElement("MESSAGE_RECEIVER_ID", receiverid));
        root1.Add(new XElement("MESSAGE_CREATION_DATE", creationDate));


        root2.Add(new XElement("MESSAGE_BODY", body));
        root2.Add(new XElement("MESSAGE_SENDER_ID", senderid));
        root2.Add(new XElement("MESSAGE_RECEIVER_ID", receiverid));
        root2.Add(new XElement("MESSAGE_CREATION_DATE", creationDate));

        if (doc1.Root.Element(root1.Name.LocalName) == null)
        {
            doc1.Element("root").Add(root1);
        }
        if (doc2.Root.Element(root2.Name.LocalName) == null)
        {
            doc2.Element("root").Add(root2);
        }
        doc1.Save(path1);
        doc2.Save(path2);
    }

but the original element are being replaced i want my xml file to look like this :

   <root>
   <Friend_2>
    <MESSAGE_BODY>hi</MESSAGE_BODY>
     <MESSAGE_SENDER_ID>1</MESSAGE_SENDER_ID>
     <MESSAGE_RECEIVER_ID>2</MESSAGE_RECEIVER_ID>
    <MESSAGE_CREATION_DATE>2014-08-29T15:33:18.1191004+03:00</MESSAGE_CREATION_DATE>
    <MESSAGE_BODY>how r you ?</MESSAGE_BODY>
    <MESSAGE_SENDER_ID>1</MESSAGE_SENDER_ID>
   <MESSAGE_RECEIVER_ID>2</MESSAGE_RECEIVER_ID>
   <MESSAGE_CREATION_DATE>2014-10-29T15:33:18.1191004+03:00</MESSAGE_CREATION_DATE>
  </Friend_2>
 </root>

my main reason to have this schema is because i am using a function that parse the document and return a dataTable containing 4 columns and 2 rows

public static DataSet ConvertXMLToDataTable(string xmlString)
{
    DataSet dataset = new DataSet();
    dataset.ReadXml(xmlString);
    return dataset.Tables.Count > 0 ? dataset : null;
}
DataSet Chat_ds=Convertor.ConvertXMLToDataTable(path);
            if (Chat_ds.Tables.Count > 0)
            {
                DataTable Chat_dt = Chat_ds.Tables["Friend_" + FriendID];
...................