XPathNavigator lnav = lnodeDoc.CreateNavigator();
XPathExpression lexp = lnav.Compile("/document/data");
lexp.AddSort("@id", XmlSortOrder.Ascending, XmlCaseOrder.None, "", XmlDataType.Text);
XPathNodeIterator lnodeIterator = lnav.Select(lexp);
string lsDocTmp = string.Empty;
while (lnodeIterator.MoveNext())
    lsDocTmp = lsDocTmp + lnodeIterator.Current.OuterXml;
lnodeDoc.InnerXml = lsDocTmp;