jsTree jQuery plugin vs Codeigniter (nodes with children not showing up)

You can use this code.

HTML Code:
<ul>
    <li>Business
        <ul>
            <li>Leo Rodriguez</li>
        </ul>
    </li>
    <li>Computer Science
        <ul>
            <li>Harry Jones</li>
            <li>Sabi</li>
        </ul>
    </li>
    </li>
    <li>IT
        <ul>
            <li>Tim Ben</li>
        </ul>
    </li>
    <li>Marketing
        <ul>
            <li>John Doe</li>
        </ul>
    </li>
</ul>

PHP Code:

<ul>
  <?php foreach ($users as $key => $value) { ?>
      <?php if($users[$key]['department'] != $users[$key-1]['department']) { ?>
           <li><?php echo $users[$key]['department']; ?></li>
           <ul>
             <li><?php echo $users[$key]['fullname']; ?></li>
           </ul>
      <?php } else { ?>
 
    <ul>  
       <li>Sabi</li>
     </ul>
  <?php } ?>
  <?php } ?>
</ul>