title: Before inserting new element in xml check if exists the value
body: <p>I have below a xml file with the below format:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8" ?&gt;
  &lt;Root&gt;
  &lt;Countries&gt;
      &lt;country&gt;India&lt;/country&gt;
      &lt;country&gt;USA&lt;/country&gt;  
      &lt;country&gt;UK&lt;/country&gt;      
  &lt;/Countries&gt;
  &lt;/Root&gt;
  
  string newCountry="UAE"
  </code></pre>
  
  <p>I want to insert this "UAE" country to the above xml file, before that I want to check whether "UAE" is already exists in the xml. If not exists then only want to insert otherwise no operation. How can I do this?</p>