Montar XML com base em arrays multidimensionais, mantendo sua estrutura

MakeDomXml.php

<?php
class MakeDomXml{
    public  $dom;
    public  $output ;
    function __construct(){
		$options = func_get_args();
		
        $this->dom  = new DOMDocument('1.0', 'UTF-8');
        $this->dom->formatOutput  = true;
        $this->dom->preserveWhiteSpace  = false;
		
		if(is_array($options[0])){
		    $this->output = $this->setElement($options[0]);
		}
    }
	public function __toString() {
		foreach ($this->output as $value) {
            $this->dom->appendChild($value);
        } 
        return $this->dom->saveXML();
    }
    public function setElement(Array $arg){
        $return = array();
        foreach ($arg as $key => $value) {
            if($value != ''){
                if(is_array($value)){
                    $elemts = $this->setElement($value);
                    $father = $this->dom->createElement($key); 
                    if(is_array($elemts)){
                        foreach ($elemts as $element) {
                            $father->appendChild($element) ;
                        }
                    }
                    $return[] = $father;
                } else {
 
                    $return[] = $this->dom->createElement($key, $value); 
                }
            } else {
                $return[] = $this->dom->createElement($key); 
            }
        }
 
        return $return;
    }
	
	public function make(Array $arg){
	    $this->output = $this->setElement($arg);
	}
}

$teste = array('smart' => array('usuario' => array('id' => 10)), 'teste' => 'aaaa');

$monta = new MakeDomXml($teste);

echo $monta;