Reading - Writing XML dynamicly in PHP - php

Question

I've following problem:
I am reading from a existing xml-file like this:
<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);
//Deks.
$xml = simplexml_load_file( "FILE" ) or die (" Couldnt load. ");
foreach ($xml->children() as $one){
foreach ($one->children() as $two ){
foreach($two->children() as $three ){
$array = array();
foreach ($three as $key => $value ){
$array[ ( string ) $key ] = ( string )$value;
echo $key . ' = ' . $value . '<br />';
}
}
}
}
?>
So I get my needed output.
My XML looks like this:
<overx>
<overy>
<katx>
<katy>
<rnd>true</rndm>
</katy>
<rely>
<lwm>true</lwm>
</rely>
</katx>
</overy>
</overy>
The xml-file is shortened heavily. Most of children have different names also their children has.
Now I want to create a html form which reads the xml form dynamically.
That's the way I am doing it:
<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);
$form_fields = null;
$xml = simplexml_load_file( "FILE" ) or die (" Couldnt load. ");
foreach ( $xml->children() as $one){
foreach ( $one->children() as $two ){
foreach( $two->children() as $three ){
$array = array();
foreach ( $three as $field ){
$form_fields .= '<div>';
$form_fields .= '<label>' . ucfirst($field->getName()) . ' </label>';
if ($field->getName() == "active" ){
$form_fields .= '<input type="checkbox" value="true"'.$field->getName() . '" />';
}
else{
$form_fields .= '<input type="text" name="'.$field->getName() . '" />';
}
$form_fields .= '</div>';
}
}
}
}
?>
But now I have the following problem:
I want to save the form as .xml which have exactly the same structure as the XML it's loaded from. Actually, I am saving poorly via javascript and right now it's only saving key->value but not the structure or anything else and I really don't know how to do it.
Thanks in advance.