<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>vue-tree-navigation</title>

  <script src="https://cdn.jsdelivr.net/npm/vue@2.5.17/dist/vue.js"></script>
  <script src="./vue-tree-navigation.js"></script>
</head>

<body>
  <div id="app">
    <vue-tree-navigation :items="items" :default-open-level="2"></vue-tree-navigation>
  </div>

  <script>
    Vue.u