JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css">
<div class="just-padding">

<div class="list-group list-group-root well">
  
  <a href="#" class="list-group-item">Item 1</a>
  <div class="list-group">
    
    <a href="#" class="list-group-item">Item 1.1</a>
    <div class="list-group">
      <a href="#" class="list-group-item">Item 1.1.1</a>
      <a href="#" class="list-group-item">Item 1.1.2</a>
      <a href="#" class="list-group-item">Item 1.1.3</a>
    </div>
    
    <a href="#" class="list-group-item">Item 1.2</a>
    <div class="list-group">
      <a href="#" class="list-group-item">Item 1.2.1</a>
      <a href="#" class="list-group-item">Item 1.2.2</a>
      <a href="#" class="list-group-item">Item 1.2.3</a>
    </div>
    
    <a href="#" class="list-group-item">Item 1.3</a>
    <div class="list-group">
      <a href="#" class="list-group-item">Item 1.3.1</a>
      <a href="#" class="list-group-item">Item 1.3.2</a>
      <a href="#" class="list-group-item">Item 1.3.3</a>
    </div>
    
  </div>
  
  <a href="#" class="list-group-item">Item 2</a>
  <div class="list-group">
    
    <a href="#" class="list-group-item">Item 2.1</a>
    <div class="list-group">
      <a href="#" class="list-group-item">Item 2.1.1</a>
      <a href="#" class="list-group-item">Item 2.1.2</a>
      <a href="#" class="list-group-item">Item 2.1.3</a>
    </div>
    
    <a href="#" class="list-group-item">Item 2.2</a>
    <div class="list-group">
      <a href="#" class="list-group-item">Item 2.2.1</a>
      <a href="#" class="list-group-item">Item 2.2.2</a>
      <a href="#" class="list-group-item">Item 2.2.3</a>
    </div>
    
    <a href="#" class="list-group-item">Item 2.3</a>
    <div class="list-group">
      <a href="#" class="list-group-item">Item 2.3.1</a>
      <a href="#" class="list-group-item">Item 2.3.2</a>
      <a href="#" class="list-group-item">Item 2.3.3</a>
    </div>
    
  </div>
  
  
  <a href="#"...

CSS

.just-padding {
  padding: 15px;
}

.list-group.list-group-root {
  padding: 0;
  overflow: hidden;
}

.list-group.list-group-root .list-group {
  margin-bottom: 0;
}

.list-group.list-group-root .list-group-item {
  border-radius: 0;
  border-width: 1px 0 0 0;
}

.list-group.list-group-root > .list-group-item:first-child {
  border-top-width: 0;
}

.list-group.list-group-root > .list-group > .list-group-item {
  padding-left: 30px;
}

.list-group.list-group-root > .list-group > .list-group > .list-group-item {
  padding-left: 45px;
}