How do I append new element to existing xml using vtd-xml in java

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XML

Java

Here is my current xml file,

<MainRoot xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<Root>
<RootElement name="rootelement1" date="21.Nov">
<SubElement id="32"/>
</RootElement>
<RootElement name="rootelement2" date="1.Dec">
<SubElement id="45"/>
</RootElement>
<RootElement name="rootelement3" date="18.Dec">
<SubElement id="12"/>
</RootElement>
</Root>
</MainRoot>

I need a java code with vtd-xml parse to append a new RootElement tag with its SunElement tag
Here is my java code

public static void main(String[] args) {
		VTDGen vtdGenerator;
		VTDNav vtdNavigator;
		XMLModifier xmlModifier;
		AutoPilot autoPilot;
		vtdGenerator = new VTDGen();
		if (vtdGenerator.parseFile("test.xml", false)) {
			vtdNavigator = vtdGenerator.getNav();
			autoPilot = new AutoPilot(vtdNavigator);
			autoPilot.bind(vtdNavigator);
			autoPilot.selectElement("RootElement");
			xmlModifier = new XMLModifier();
			while (autoPilot.iterate()) {
				// code to insert new RootElement tag with its subElment tag and
				// their atributes
			}
		}
		xmlModifier.output(new FileOutputStream("test.xml"));
	}

I can insert single tag using this

xmlModifier.insertAfterElement("<RootElement name=\"rootelement4\" date=\"21.Dec\">\n\t\t<SubElement id=\"66\"/>\n</RootElement>");

but I want to insert multiple RootElement tags which is now allowed by this process.
can anyone help me on this to append multiple tags to an xml. Is there any other approach to this.
I don't want to use DOM parser, as the order of attributes are not guaranteed with DOM.

I need output like this

<MainRoot xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<Root>
<RootElement name="rootelement1" date="21.Nov">
<SubElement id="32"/>
</RootElement>
<RootElement name="rootelement2" date="1.Dec">
<SubElement id="45"/>
</RootElement>
<RootElement name="rootelement3" date="18.Dec">
<SubElement id="12"/>
</RootElement>
<RootElement name="rootelement4" date="21.Dec">
<SubElement id="66"/>
</RootElement>
</Root>
</MainRoot>