Writing to an XML File?

I simply want to add a element to an already existing element in an XML file through javascript. Here is my code:

     function WriteToXmlFile(){
          var xmlDoc : XmlDocument = new XmlDocument();
          xmlDoc.Load(Application.dataPath + "/data/saveWorld.xml");
          elmRoot = xmlDoc.DocumentElement;
     
          element = xmlDoc.CreateElement("block");
          attribute = xmlDoc.CreateAttribute("ID");    
          elmRoot.AppendChild(element);            //append "block" element to "blocks" element    
 
          xmlDoc.Save(Application.dataPath + "/data/saveWorld.xml");
 
 }

Like I said before I create an element called "block" then I want to make it a child of the root element (which btw is called "blocks"). Therefore the whole document should look like this:

But for some reason it doesn't, instead the script makes it looks like this:

Why does this happen and how can I fix it to look like the first tree?

Thanks!