Demo - Wijmo TreeView

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css">
<link rel="stylesheet" href="https://cdn.grapecity.com/wijmo/5.latest/styles/wijmo.min.css">
<script src="https://cdn.grapecity.com/wijmo/5.latest/controls/wijmo.min.js"></script>
<script src="https://cdn.grapecity.com/wijmo/5.latest/controls/wijmo.nav.min.js"></script>
<div class="container">

  <div id="theTree"></div>
  
  <div id="selection"></div>
  <div id="click"></div>
</div>

CSS

/* default trees on this sample */
.wj-treeview {
    display:block;
    //height: 350px;
    font-size: 120%;
    margin-bottom: 8px;
    padding: 6px;
    background: #f0f0f0;
    box-shadow: 0 3px 6px rgba(0,0,0,0.16), 0 3px 6px rgba(0,0,0,0.23);
}
body {
  margin-bottom: 24pt;
}

.wj-node select{
  float: right;
}
.wj-treeview .wj-nodelist .wj-node:before { 
    border: none;
}
.wj-treeview .wj-nodelist > .wj-nodelist > .wj-node,
.wj-treeview .wj-nodelist > .wj-nodelist > .wj-nodelist {
    font-size: 100%;
    border-left: 1px dashed ;
}

.separator::before {
    content: '--';
    margin-left: -10px;
    color: black;
}

JavaScript

onload = function() {

//var oldFn = wijmo.nav.TreeNode.prototype.setChecked;
wijmo.nav.TreeNode.prototype.setChecked = function(checked) {
    let cb = this.checkBox;
        cb.checked = checked;
        cb.indeterminate = false;
}

  // create the tree
  var tree = new wijmo.nav.TreeView('#theTree', {
    itemsSource: getData(),
    displayMemberPath: 'header',
    childItemsPath: 'items',
    showCheckboxes: true,
    checkOnClick: false,
    selectedItemChanged: function(s, e) {
      var msg = wijmo.format('You selected item <b>{header}</b>.', s.selectedItem);
      document.getElementById('selection').innerHTML = msg;
    },
    itemClicked: function(s, e) {
      var msg = wijmo.format('You clicked item <b>{header}</b>.', s.selectedItem);
      document.getElementById('click').innerHTML = msg;
    },
    formatItem: function (s, e) {
        if (e.dataItem.newItem) {
            e.element.innerHTML += 
                '<select style="margin-left:6px"><option value="item 1">item1</option><option value="item 2">item2</option></select>';
            var el = e.element.querySelector("select");
            el.addEventListener("click", function(e){
              e.preventDefault();
              e.stopPropagation();
            });
        }
        
        if (e.level != 0) {
        	var oldHTML = e.element.innerHTML, span = '';
        span = `<span class="separator"></span>`;
        e.element.innerHTML = span + oldHTML;
        }
    }
  });
  
  tree.removeEventListener(tree.hostElement, 'keydown');
 // window["tree"] = tree;
  
  // get the tree data
  function getData() {
    return [
      { header: 'Electronics', img: 'resources/electronics.png', items: [
        { header: 'Trimmers/Shavers' },
        { header: 'Tablets' },
        { header: 'Phones', img: 'resources/phones.png', items: [
          { header: 'Apple', items: [
          { header: 'Apple', items: [
          { header: 'Apple' },
          { header: 'Motorola', newItem: true },
       ...