Edit in JSFiddle

.group {
    background: yellow;
    width: 200px;
    height: 500px;
}
.group .subgroup {
    background: orange;
    width: 150px;
    height: 200px;
}
.fixed {
    position: fixed;
}

/* sidebar */
.bs-docs-sidebar {
    padding-left: 20px;
    margin-top: 20px;
    margin-bottom: 20px;
}

/* all links */
.bs-docs-sidebar .nav>li>a {
    color: #999;
    padding: 4px 20px;
    font-size: 13px;
    font-weight: 400;
}

/* nested links */
.bs-docs-sidebar .nav .nav>li>a {
    padding-top: 1px;
    padding-bottom: 1px;
    padding-left: 30px;
    font-size: 12px;
}

<div class="row">
    <!--Nav Bar -->
    <nav class="col-xs-3 bs-docs-sidebar">
        <ul id="sidebar" class="nav nav-stacked fixed">
            <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 id="GroupC" class="group">
            <h3>Group C</h3>
            <div id="GroupCSub1" class="subgroup">
                <h4>Group C Sub 1</h4>
            </div>
            <div id="GroupCSub2" class="subgroup">
                <h4>Group C Sub 2</h4>
            </div>
        </section>    
    </div>
</div>