Hello,
Here is the code you have to write in your onClick Event,
IXMLDOMDocument2 sampleDataDom = (IXMLDOMDocument2)thisXDocument.CreateDOM();
sampleDataDom.async = false;
sampleDataDom.validateOnParse = false;
sampleDataDom.setProperty("SelectionNamespaces", "namespace of your form");
sampleDataDom.load("sampledata.xml");
IXMLDOMNode perActivityNodeFromSampledata = sampleDataDom.selectSingleNode("/my:TimesheetDetails/my:EmployeeInformation/my:TimeReporting/my:PerActivity").cloneNode(true);
IXMLDOMNode timeReportingNode = thisXDocument.DOM.selectSingleNode("("/my:TimesheetDetails/my:EmployeeInformation/my:TimeReporting ");
//Inserting the sample node at first position.
timeReportingNode.parentNode.insertBefore(perActivityNodeFromSampledata, timeReportingNode);