title: How to add XML child nodes to multiple parent nodes
body: <p>I have an xml file like this.</p>
  
  <pre><code>&lt;ArrayOfALternateUnitModel&gt;
  &lt;ALternateUnitModel&gt;
  &lt;UnitId&gt;1048&lt;/UnitId&gt;
  &lt;Name&gt; CARTON&lt;/Name&gt;
  &lt;/ALternateUnitModel&gt;
  
  &lt;ALternateUnitModel&gt;
  &lt;UnitId&gt;2063&lt;/UnitId&gt;
  &lt;Name&gt; PACKET&lt;/Name&gt;
  &lt;/ALternateUnitModel&gt;
  &lt;/ArrayOfALternateUnitModel&gt;
  </code></pre>
  
  <p>what i need is.</p>
  
  <pre><code>&lt;ArrayOfALternateUnitModel&gt;
  &lt;ALternateUnitModel&gt;
  &lt;UnitId&gt;1048&lt;/UnitId&gt;
  &lt;Name&gt; CARTON&lt;/Name&gt;
  &lt;NewChild&gt;new child&lt;/NewChild&gt;
  &lt;/ALternateUnitModel&gt;
  
  &lt;ALternateUnitModel&gt;
  &lt;UnitId&gt;2063&lt;/UnitId&gt;
  &lt;Name&gt; PACKET&lt;/Name&gt;
  &lt;NewChild&gt;new child&lt;/NewChild&gt;
  &lt;/ALternateUnitModel&gt;
  &lt;/ArrayOfALternateUnitModel&gt;
  </code></pre>
  
  <p>My code looks like this.</p>
  
  <pre><code>xmlDoc.Load(xmlStream);
  XmlElement childElement = xmlDoc.CreateElement("NewChild");
  childElement.InnerText = "new child";
  XmlNode parentNode = xmlDoc.SelectSingleNode("ArrayOfALternateUnitModel/ALternateUnitModel");
  parentNode.AppendChild(childElement);
  </code></pre>
  
  <p>Output goes like this.</p>
  
  <pre><code>&lt;ArrayOfALternateUnitModel&gt;
  &lt;ALternateUnitModel&gt;
  &lt;UnitId&gt;1048&lt;/UnitId&gt;
  &lt;Name&gt; CARTON&lt;/Name&gt;
  &lt;NewChild&gt;new child&lt;/NewChild&gt;
  &lt;/ALternateUnitModel&gt;
  
  &lt;ALternateUnitModel&gt;
  &lt;UnitId&gt;2063&lt;/UnitId&gt;
  &lt;Name&gt; PACKET&lt;/Name&gt;
  &lt;/ALternateUnitModel&gt;
  &lt;/ArrayOfALternateUnitModel&gt;
  </code></pre>
  
  <p>In the second node its not adding child nodes. How to add child to all parent nodes?</p>