title: create a node in a xml document if it does not exist using linq to xml
body: <p>I am querying a xml document using the XPathSelectElement method.</p>
  
  <p>if the node does not exist I would like to insert a node with that path in the same document. The parent nodes should also be created if they do not exist. Is there an easy way to do this without looping through the parents checking if they exist? (Add a new node using XPath)</p>