Append XML string block to existing XmlDocument

I have an XmlDocument that already exists and is read from a file.

I would like to add a chunk of Xml to a node in the document. Is there a good way to create and add all the nodes without cluttering my code with many .CreateNote and .AppendChild calls?

I would like some way of making a string or stringBuilder of a valid Xml section and just appending that to an XmlNode.

ex:Original XmlDoc:

<MyXml><Employee></Employee></MyXml>

and, I would like to add a Demographic (with several children) tag to Employee:

<MyXml><Employee><Demographic><Age/><DOB/></Demographic></Employee></MyXml>