JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
  <li>a1</li>
  <li>a2</li>
  <li>a3</li>
  <li class="sub">s1</li>
  <li class="sub">s2</li>
  <li class="sub">s3</li>
  <li>b1</li>
  <li>b2</li>
  <li class="sub">c1</li>
  <li class="sub">c2</li>
  <li class="sub">c3</li>
  <li></li>
 </ul>

CSS

.sub {
    color:red;
}

JavaScript

$('.sub').each(function() {
    if ($(this.parentNode).hasClass('wrapped')) return;
        $(this).nextUntil(':not(.sub)').andSelf().wrapAll('<li><ul class="wrapped">');
});