Side Navbar Submenu - Scrollspy

HTML

<link rel="stylesheet" href="//netdna.bootstrapcdn.com/bootstrap/3.0.0/css/bootstrap.min.css">
<script src="//netdna.bootstrapcdn.com/bootstrap/3.0.0/js/bootstrap.min.js"></script>
<link rel="stylesheet" href="//netdna.bootstrapcdn.com/font-awesome/3.2.1/css/font-awesome.min.css">
<div class="row">
    <!--Nav Bar -->
    <nav class="col-xs-3 bs-docs-sidebar hidden-print">
        <ul class="nav nav-stacked fixed" id="sidebar">
            <li>
                <a href="#GroupA">Group A</a>
                <ul class="nav nav-stacked" >
                    <li><a href="#GroupASub1">Sub-Group 1</a></li>
                    <li><a href="#GroupASub2">Sub-Group 2</a></li>
                </ul>
            </li>
            <li>
                <a href="#GroupB">Group B</a>
                <ul class="nav nav-stacked" >
                    <li><a href="#GroupBSub1">Sub-Group 1</a></li>
                    <li><a href="#GroupBSub2">Sub-Group 2</a></li>
                </ul>
            </li>
            <li>
                <a href="#GroupC">Group C</a>
                <ul class="nav nav-stacked" >
                    <li><a href="#GroupCSub1">Sub-Group 1</a></li>
                    <li><a href="#GroupCSub2">Sub-Group 2</a></li>
                </ul>
            </li>
        </ul>
    </nav>
    <!--Main Content -->
    <div class="col-xs-9">
        <section id="GroupA" class="group">
            <h3>Group A</h3>
            <div id="GroupASub1" class="subgroup">
                <h4>Group A Sub 1</h4>
            </div>
            <div id="GroupASub2" class="subgroup">
                <h4>Group A Sub 2</h4>
            </div>
        </section>
        <section id="GroupB" class="group">
            <h3>Group B</h3>
            <div id="GroupBSub1" class="subgroup">
                <h4>Group B Sub 1</h4>
            </div>
            <div id="GroupBSub2" class="subgroup">
                <h4>Group B Sub 2</h4>
            </div>
        </section>
        <section...

CSS

.group {
    background: yellow;
    width: 200px;
    height: 500px;
}
.group .subgroup {
    background: orange;
    width: 150px;
    height: 200px;
}
.fixed {
    position: fixed;
}
.bs-docs-sidebar {
    padding-left: 20px;
    margin-top: 20px;
    margin-bottom: 20px;
}
.bs-docs-sidebar .nav>li>a {
    display: block;
    font-size: 13px;
    font-weight: 500;
    color: #999;
    padding: 4px 20px;
}
.bs-docs-sidebar .nav>li>a:hover, 
.bs-docs-sidebar .nav>li>a:focus {
    padding-left: 19px;             /*indent from left */
    color: #563d7c;                 /*highlight color */
    text-decoration: none;          /*turn off underline */
    background-color: transparent;  /*turn off selection color */
    border-left: 1px solid #563d7c; /*add left cursor */
}

.bs-docs-sidebar .nav>.active>a, 
.bs-docs-sidebar .nav>.active:hover>a,
.bs-docs-sidebar .nav>.active:focus>a {
    padding-left: 18px;
    font-weight: 700;
    color: #563d7c;
    background-color: transparent;
    border-left: 2px solid #563d7c;
}
.bs-docs-sidebar .nav .nav {
    display: none;            /*hide nested list */
}
.bs-docs-sidebar .nav>.active>ul {
    display: block;           /*show list when active */
    padding-bottom: 10px;     /*add a little buffer */
}
.bs-docs-sidebar .nav .nav>li>a {
    padding-top: 1px;
    padding-bottom: 1px;
    padding-left: 30px;
    font-size: 12px;
    font-weight: 400;
}
.bs-docs-sidebar .nav .nav>li>a:hover,
.bs-docs-sidebar .nav .nav>li>a:focus {
    padding-left: 60px;
}
.bs-docs-sidebar .nav .nav>.active>a,
.bs-docs-sidebar .nav .nav>.active:hover>a,
.bs-docs-sidebar .nav .nav>.active:focus>a {
    font-weight: 500;
    padding-left: 28px;
    color: red;
}

JavaScript

$('body').scrollspy({
    target: '#sidebar'
});