convert xml array to nested set model

I want to take an xml file, break it down and save it to a db while preserving its hierarchy using the nested set model. I have converted the xml to an array using the following function. Is there a way to modify this function to add left and right values? Or a way to go through the result and add left and right values while collapsing the array?

<?php


function xml_to_array($root) {
    $result = array();
    $disallowed = Array('#text','#comment');


    if ($root->hasAttributes()) {
        $attrs = $root->attributes;
        foreach ($attrs as $attr) {
            $result['@attributes'][$attr->name] = $attr->value;
        }
    }

    if ($root->hasChildNodes()) {
        $children = $root->childNodes;
        if ($children->length == 1) {
            $child = $children->item(0);
            if ($child->nodeType == XML_TEXT_NODE) {
                $result['_value'] = $child->nodeValue;
                return count($result) == 1
                    ? $result['_value']
                    : $result;
            }
        }
        $groups = array();
        foreach ($children as $child) {
            if (!in_array($child->nodeName , $disallowed) ){
                if (!isset($result[$child->nodeName])) {
                    $result[$child->nodeName] = xml_to_array($child);
                } else {
                    if (!isset($groups[$child->nodeName])) {
                        $result[$child->nodeName] = array($result[$child->nodeName]);
                        $groups[$child->nodeName] = 1;
                    }
                    $result[$child->nodeName][] = xml_to_array($child);
                }
            }
        }
    }

    return $result;
}
?>

Sample xml: note- every node has attributes. I would like to save the left/right under the attribute array.

<root>
    <nodeFoo>
       <nodeBar>
           <nodeXYZ/>
           <nodeXYZ/>
           <nodeXYZ/> 
       </nodeBar>
    </nodeFoo>
       <nodeBar>
           <nodeXYZ/>
           <nodeXYZ/>
           <nodeXYZ/> 
       </nodeBar>
 </root>