How to append to an existing XML?

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C#

.NET

Hello.

I am making a serializable XML stream. I get the data from the classes and user input.
Then I go to saving method and here is my question.

Example XML:

<?xml version="1.0" encoding="UTF-8"?>
<dates>
  <date value="19-10-2014">
    <progLang value="Java">
      <Name>Java</Name>
      <Price>Free</Price>
    </progLang>
    <progLang value="Ruby">
      <Name>Ruby</Name>
      <Price>$400</Price>
    </progLang>
  </date>
  <date value="20-10-2014">
    <progLang value="C#">
      <Name>C#</Name>
      <Price>€40000</Price>
    </progLang>
  </date>
</dates>

How to add new date entry to this existing xml file?