XML element addition

I used
XmlDocument to load from a file.

Then how do I append an element to the end?

<files>
<file>
<name>graphic.txt</name>
<location>c:\temp</location>
</file>
</files>

I want to add this:
<file>
<name>editor.exe</name>
<location>c:\executable</location>
</file>


.

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