// Create XML Object
$xml = new DOMDocument("1.0", "UTF-8");

// Make a Parent Node
$dataset = $xml->createElement("dataset");
$xml->appendChild($dataset);

$data = $xml->createElement("data");
$dataset->appendChild($data);

// make child node
$data->appendChild($xml->createElement("key", $value));

// Show Data
echo $xml->saveXML();