main-menu-component.twig

<nav class="main-menu"> 
  <ul class="main-menu__items">
    {% for item in items %}
      <li class="main-menu__item{{ item.below ? ' has-submenu' }}">
        <a class="main-menu__item--link" href="{{ item.url }}">
          {{ item.title }}
        </a>
        {% if item.below %}
          <ul class="main-menu__sub-menu" id="main-menu">
            {% for sublink in item.below.items %}
              <li class="main-menu__item">
                <a href="{{ sublink.url }}">
                  {{ sublink.title }}
                </a>
              </li>
            {% endfor %}
          </ul>
        {% endif %}
      </li>
    {% endfor %}
  </ul>
</nav>