<?php foreach($form['categories'] as $fieldSchema => $embeddedForm): ?>
        <div class="checkboxSerie">
          <fieldset>
            <ul>
          <?php echo $embeddedForm->renderError(); ?>
          <?php
            $i=0;
            $secondColumn = false;
            $totalOptions = count($embeddedForm);
            foreach ($embeddedForm as $widget): ?>
              <?php
                $i++;
                if (!$secondColumn && $i >= $totalOptions/2):
                  $secondColumn = true;
              ?>
            </ul>
                </fieldset>
                <fieldset>
                  <ul>
              <?php endif; ?>
              <li>
              <?php echo $widget->render(); ?>
              <?php echo $widget->renderLabel(); ?>
              </li>
          <?php endforeach; ?>
            </ul>
          </fieldset>
        </div>
      <?php endforeach; ?>