title: Adding element to existing XML node
body: <p>Where am i going wrong???</p>
  
  <p>I have an xml file with OppDetails as a tag already as shown below</p>
  
  <pre><code>&lt;OppDetails&gt;
    &lt;OMID&gt;245414&lt;/OMID&gt; 
    &lt;ClientName&gt;Best Buy&lt;/ClientName&gt; 
    &lt;OppName&gt;International Rate Card&lt;/OppName&gt; 
    &lt;CTALinkType&gt;AO,IO,MC,TC&lt;/CTALinkType&gt; 
    &lt;/OppDetails&gt;
    &lt;/OppFact&gt;
  </code></pre>
  
  <p>Now i am trying to add another element to it but getting an error in AppendChild method please help</p>
  
  <pre><code>XmlNode rootNode = xmlDoc.SelectSingleNode("OppDetails");
  XmlElement xmlEle = xmlDoc.CreateElement("CTAStartDate");
  xmlEle.InnerText = ExcelUtility.GetCTAStartDate();
  rootNode.AppendChild(xmlEle);
              xmlDoc.Save("C:\\test.xml");
  </code></pre>