soap client calling function with parameters and type

I have soap request with body

<soap:Body>
    <ProcessRequest>
        <request xsi:type="GetNotification">
            <node1>val1</node2>
            <node2>val2</node2>
        </request>
    </ProcessRequest>
</soap:Body>

I am trying to pass request type GetNotification in soap client call in PHP but its not working. in $args I am passing

$args = ['node1' => 'val1','node2'=>'node2'];
$response = $client->ProcessRequest(['request'=>$args])

how do i pass type GetNotification

from soap client calling function with parameters and type