JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.2/css/bootstrap.min.css">
<div class="container">
    <div class="row">
        <div class="col-xs-12">
            <ul class="list-group">
                <li class="list-group-item">One</li>
                <li class="list-group-item">Two
                    <ul class="list-group inner">
                        <li class="list-group-item">Item 2a</li>
                        <li class="list-group-item">Item 2b</li>
                    </ul>
                </li>
                <li class="list-group-item">Three
                    <ul class="list-group inner">
                        <li class="list-group-item">Item 3a</li>
                        <li class="list-group-item">Item 3b</li>
                    </ul>
                </li>
            </ul>
        </div>
    </div>
</div>

CSS

.list-group.inner li{
    border:none;
    
}