how to return XmlDocument from WCF service?

We have WCF service. In that a DataTable which contains two ROWS of record. we converted that DataTable to raw XML. Now we want to return that raw XML data as XMLDocument to client.

we have method like this

public System.Xml.XmlDocument ConvertTo(DataTable data)
{
DataTable dt=new DataTable();
dt.WriteXml("Data comes from source");
return xmlDocument;

}

And the RAW XML data is like this:

<NewDataSet>
<Table1>
<ID>1</ID>
</Table1>
<Table2>
<ID>2</ID>
</Table2>
</NewDataSet>

Give us suggestion how to return the RAW XML data as XMLDocument to the Client from WCF?

Nayan