Unable to produce correct XML from PHP

I have written this code to generate this XML structure, but for some reason it doesn't seems to be working. It throws the error :- Undefined variable: operationtype in C:\wamp\www\sms-gateway\dev\testxml.php on line 11 and Call to a member function appendChild() on a non-object in C:\wamp\www\sms-gateway\dev\testxml.php on line 11

I'm using php's DOMDocument library, which I don;t have any experience with. Here's what I need to generate :-

Here's my code :-

function gen_xml($number,$message,$smssender)
{
    /* create a dom document with encoding utf8 */
    $domtree = new DOMDocument('1.0', 'UTF-8');

    /* create the root element of the xml tree */
    $xmlRoot = $domtree->createElement("sms-teknik");
    /* append it to the document created */
    $xmlRoot = $domtree->appendChild($xmlRoot);


    $operationtype->appendChild($domtree->createElement('operationtype','0'));
    $flash->appendChild($domtree->createElement('flash','0'));
    $multisms->appendChild($domtree->createElement('multisms','0'));
    $maxmultisms->appendChild($domtree->createElement('maxmultisms','0'));
    $compresstext->appendChild($domtree->createElement('compresstext','0'));
    $smssender->appendChild($domtree->createElement('smssender',$smssender));
    $deliverystatustype->appendChild($domtree->createElement('deliverystatustype','0'));
    $usereplynumber->appendChild($domtree->createElement('usereplynumber','0'));
    $usereplyforwardtype->appendChild($domtree->createElement('usereplyforwardtype','0'));
    $usee164->appendChild($domtree->createElement('usee164','0'));


    $item=$domtree->createElement("items");
    $item = $domtree->appendChild($item);

    $recipient = $domtree->createElement("recipient");
    $recipient = $domtree->appendChild($recipient);

    $orgaddress->appendChild($domtree->createElement('orgaddress',$number));
    echo $domtree->saveXML();
}

Any suggestions / help would be greatly appreciated.