JSFiddle - React, Tailwind, and code Playground

HTML

<ul class="menu">
  <li>
    <a href=#>item1</a>
    <ul class="sub-ul-1">
      <li><a>subitem1</a></li>
      <li><a>subitem2</a></li>
      <li><a>subitem3</a></li>
      <li><a>subitem4</a></li>
      <li>
        <a href=#>item2</a>
        <ul class="sub-ul-2">
          <li><a>subitem5</a></li>
          <li><a>subitem6</a></li>
          <li><a>subitem7</a></li>
          <li><a>subitem8</a></li>
        </ul>
      </li>
    </ul>
  </li>
</ul>

CSS

/* Hide all UL's inside .menu */
.menu ul {
    display: none;
}

/* Show any UL which is a direct child of a hovered list-item. */
.menu li:hover > ul {
    display: block;
}