PHP SimpleXML-多个子级同名

我目前正在用以下php代码生成一个xml文件。它接受表单输入并将其放入xml文件中。

我想有多个同名的孩子。如:

<person>
  <address>
    <street>streetname</street>
    <streetnumber>streetnumber</streetnumber>
  </address>
  <address>
    <street>streetname</street>
    <streetnumber>streetnumber</streetnumber>
  </address>
</person>  

我生成xml的代码遵循这种结构;

//Add first address - working

$xml->person = "";
$xml->person->address = "";

$xml->person->address->addChild('streetname', $_POST['streetname1']);
$xml->person->address->addChild('streetnumber', $_POST['streetnumber1']);


//Attempt to add second address, doesn't work

$xml->person->address = "";

$xml->person->address->addChild('streetname', $_POST['streetname2']);
$xml->person->address->addChild('streetnumber', $_POST['streetnumber2']);