W3Schools Tryit Editor

<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<style>
ul, #myUL {
  list-style-type: none;
}

#myUL {
  margin: 0;
  padding: 0;
}

.box {
  cursor: pointer;
  -webkit-user-select: none; /* Safari 3.1+ */
  -moz-user-select: none; /* Firefox 2+ */
  -ms-user-select: none; /* IE 10+ */
  user-select: none;
}

.box::before {
  content: "\2610";
  color: black;
  display: inline-block;
  margin-right: 6px;
}

.check-box::before {
  content: "\2611"; 
  color: dodgerblue;
}

.nested {
  display: none;
}

.active {
  display: block;
}
</style>
</head>
<body>

<h2>Tree View</h2>
<p>A tree view represents a hierarchical view of information, where each item can have a number of subitems.</p>
<p>Click on the box(es) to open or close the tree branches.</p>

<ul id="myUL">
  <li><span class="box">Beverages</span>
    <ul class="nested">
      <li>Water</li>
      <li>Coffee</li>
      <li><span class="box">Tea</span>
        <ul class="nested">
          <li>Black Tea</li>
          <li>White Tea</li>
          <li><span class="box">Green Tea</span>
            <ul class="nested">
              <li>Sencha</li>
              <li>Gyokuro</li>
              <li>Matcha</li>
              <li>Pi Lo Chun</li>
            </ul>
          </li>
        </ul>
      </li>  
    </ul>
  </li>
</ul>

for (i = 0; i < toggler.length; i++) {
  toggler[i].addEventListener("click", function() {
    this.parentElement.querySelector(".nested").classList.toggle("active");
    this.classList.toggle("check-box");
  });
}
</script>

</body>
</html>