Problem with XML format after insert a new XMLNode

In my node app I have to insert a new XMLnode for identify it later. I developed some code where I expected the right result.
It is really simple:

var xmlDoc = new DOMParser().parseFromString(dataRegelWerk);  //Incomming data
if(allok == false){
                var root = xmlDoc.documentElement;

                var varselem = xmlDoc.getElementsByTagName('vars')[0];
                var newEle = xmlDoc.createElement('TCafe');
                var att1 = xmlDoc.createAttribute("initvalue");
                att1.value = "1";
                var att2 = xmlDoc.createAttribute("type");
                att2.value = "int";
                newEle.setAttributeNode(att1);
                newEle.setAttributeNode(att2);

                root.insertBefore(newEle, varselem);
            }

var myFile = serializer.serializeToString(xmlDoc); //Put back to string to store in db

This is the original formatted XML

<xml xmlns:xi="http://www.w3.org/2001/XInclude">

   <vars>
....

I tried to insert before "vars" and the result is

<xml xmlns:xi="http://www.w3.org/2001/XInclude">

    <TCafe initvalue="1" type="int"/><vars>

But I expected

<xml xmlns:xi="http://www.w3.org/2001/XInclude">

    <TCafe initvalue="1" type="int"/>

       <vars>

Is there anything wrong with my code or do I expect a wrong thing? Maybe I have to close the new XMLNode? (I expected the last / will do it.
Any help will be great.