How to print these results in html unordered list form in stead of xml?

I have a php script that takes hierarchical data from a mysql procedure and prints it as xml. I want to these results to be printed as html unordered parent child list. How do I do that. Here is my php script that prints xml:

  <?php
      header("Content-type: text/xml");
      $conn = new mysqli("localhost", "user", "********", "spec", 3306);

      // one non-recursive db call to get the message tree !
      $result = $conn->query("call message_hier(1)");

      //--$result = $conn->query("call message_hier_all()");

      $xml = new DomDocument;
      $xpath = new DOMXpath($xml);

      $msgs = $xml->createElement("messages");
      $xml->appendChild($msgs);

      // loop and build the DOM
      while($row = $result->fetch_assoc()){
       $msg = $xml->createElement("message");
       foreach($row as $col => $val) $msg->setAttribute($col, $val); 

      if(is_null($row["parent_msg_id"])){
        $msgs->appendChild($msg);
       }
      else{
        $qry = sprintf("//*[@msg_id = '%d']", $row["parent_msg_id"]);
        $parent = $xpath->query($qry)->item(0);
        if(!is_null($parent)) $parent->appendChild($msg);
        }
      }
      $result->close();
      $conn->close();
      echo $xml->saveXML();
      ?>

this is xml it prints

<messages>
    <message msg_id="1" emp_msg="msg 1" parent_msg_id="" parent_msg="" depth="0">
        <message msg_id="2" emp_msg="msg 1-1" parent_msg_id="1" parent_msg="msg 1" depth="1"/>
        <message msg_id="3" emp_msg="msg 1-2" parent_msg_id="1" parent_msg="msg 1" depth="1">
            <message msg_id="4" emp_msg="msg 1-2-1" parent_msg_id="3" parent_msg="msg 1-2" depth="2"/>
            开发者_C百科<message msg_id="5" emp_msg="msg 1-2-2" parent_msg_id="3" parent_msg="msg 1-2" depth="2">
                <message msg_id="6" emp_msg="msg 1-2-2-1" parent_msg_id="5" parent_msg="msg 1-2-2" depth="3">
                    <message msg_id="7" emp_msg="msg 1-2-2-1-1" parent_msg_id="6" parent_msg="msg 1-2-2-1" depth="4"/>
                    <message msg_id="8" emp_msg="msg 1-2-2-1-2" parent_msg_id="6" parent_msg="msg 1-2-2-1" depth="4"/>
                </message>
            </message>
        </message>
    </message>
</message

XSLT:

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
    xmlns:html="http://www.w3.org/1999/xhtml">
  <xsl:output omit-xml-declaration="yes" />

  <xsl:template match="messages">
    <html:ul>
      <xsl:apply-templates select="message" />
    </html:ul>
  </xsl:template>

  <xsl:template match="message[message]">
    <html:li>message <xsl:value-of select="@msg_id" /></html:li>
    <html:ul>
      <xsl:apply-templates select="message" />
    </html:ul>
  </xsl:template>

  <xsl:template match="message">
    <html:li>message <xsl:value-of select="@msg_id" /></html:li>
    <xsl:apply-templates select="message" />
  </xsl:template>
</xsl:stylesheet>