Recursive menu/submenu list from wp_get_nav_menu_items. Change menu name and style to your needs. Supports unlimited number of submenus.

wp-recursive-menu.php

<?php
  $menu_name = 'menu-name';
  $locations = get_nav_menu_locations();
  $menu = wp_get_nav_menu_object( $locations[ $menu_name ] );
  $menuitems = wp_get_nav_menu_items( $menu->term_id, array( 'order' => 'DESC' ) );

//echo '<pre>'.print_r($menuitems).'</pre>';

function buildTree( array &$elements, $parentId = 0 )
{
    $branch = array();
    foreach ( $elements as &$element )
    {
        if ( $element->menu_item_parent == $parentId )
        {
            $children = buildTree( $elements, $element->ID );
            if ( $children )
                $element->child = $children;
                $element->has_children = 1;

            $branch[$element->ID] = $element;
            unset( $element );
        }
    }
    return $branch;
}
$menuitems = buildTree($menuitems);

function create_menu($item) {
    $link = $item->url;
    $title = $item->title;
    $id = $item->ID;
    
    if(property_exists($item, 'child')) {
        $children = $item->child;
        ?>
        <li class="menu-item menu-item-<?php echo $id; ?> menu-has-children">
            <div>
                <?php echo $title; ?>&nbsp;<i class="fa fa-angle-double-down" aria-hidden="true"></i>
            </div>
            <ul class="dropdown-menu">
            <?php 
            foreach($children as $child){
                create_menu($child);
            }
            ?>
            </ul>
        </li>
    <?php
    } else {
    ?>
        <li class="menu-item menu-item-<?php echo $id; ?>">
            <a href="<?php echo $link; ?>">
                <?php echo $title; ?>
            </a>
        </li>
    <?php
    }
}

?>

<ul class="nav-ul">
    <?php
    foreach( $menuitems as $item ){
        create_menu($item);
    }
    ?>
</ul>