<?php
$parent_categories = get_categories( array(
'orderby' => 'slug',
'order' => 'ASC',
'parent' => 0
) );
foreach( $parent_categories as $parent_category ) {
?>
<li>
<span class="btn btn-navbar">
<?php echo $parent_category->name ?> <i class="fa fa-caret-down" aria-hidden="true"></i>
<ul class="card-menu">
$categories = get_categories( array(
'parent' => $parent_category->term_id
foreach( $categories as $category ) {
if ($category->slug != "chapters") {
echo '<li><a class="menu-element" href="' . get_category_link($category->term_id) . '">' . $category->name . '</a></li>';
}
</ul>
</span>
</li>