XmlDocument.Save() - Automatic indenting?

Hi

I've added a new Xml-node to my XmlDocument:

XmlDocument xml = newXmlDocument();
xml.Load("books.xml");
XmlNode fragment = xml.CreateDocumentFragment();
fragment.InnerXml = "<Book><Title>MyBook</Title></Book>";
xml.DocumentElement.AppendChild(fragment);
xml.Save("books.xml");

The problem is that the added node is not correctly indented.
I want the output to be:

<Book>
  <Title>
    MyBook
  </Title>
</Book>

How do I do this?

Kind Regards