View index.html
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width">
<title>Example nested dropdown</title>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/materialize/0.98.2/css/materialize.min.css" />
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/materialize/0.98.2/js/materialize.min.js"></script>
<style>