階層のある目次などで見やすくするために下位の階層を折りたたみ（collapse）の機能で表示、非表示を切替えられると便利です。Bootstrap3の標準機能でリスト、リストグループ、パネルの階層を折りたたみ設定してみました。
リストを折りたたみ
<ol>
<li>
<a data-toggle="collapse" href="#list1">
目次１
</a>
<div id="list1" class="panel-collapse collapse">
<div class="panel-body">
<ol>
<li>
<a data-toggle="collapse" href="#list11">
目次１－１
</a>
<div id="list11" class="panel-collapse collapse">
<div class="panel-body">
<ol>
<li>目次１－１－１</li>
<li>目次１－１－２</li>
<li>目次１－１－３</li>
</ol>
</div>
</div>
</li>
<li>目次１－２</li>
<li>目次１－３</li>
</ol>
</div>
</div>
</li>
<li>目次２</li>
<li>目次３</li>
<li>目次４</li>
</ol>
パネルグループを折りたたみ
<div class="panel-group">
<div class="panel panel-default">
<div class="panel-heading">
<h4 class="panel-title">
<a data-toggle="collapse" href="#acc1">
目次１
</a>
</h4>
</div>
<div id="acc1" class="panel-collapse collapse">
<div class="panel-body">
<div class="panel-group">
<div class="panel panel-default">
<div class="panel-heading">
<h4 class="panel-title">
<a data-toggle="collapse" href="#acc11">
目次１ー１
</a>
</h4>
</div>
<div id="acc11" class="panel-collapse collapse">
<div class="panel-body">
<div class="panel-group">
<div class="panel panel-default">
<div class="panel-heading">
<h4 class="panel-title">
<a data-toggle="collapse" href="#acc111">
目次１ー１－１
</a>
</h4>
</div>
<div id="acc111" class="panel-collapse collapse">
<div class="panel-body">
</div>
</div>
</div>
<div class="panel panel-default">
<div class="panel-heading">
<h4 class="panel-title">
<a data-toggle="collapse" href="#acc112">
目次１－１－２
</a>
</h4>
</div>
<div id="acc112" class="panel-collapse collapse">
<div class="panel-body">
</div>
</div>
</div>
<div class="panel panel-default">
<div class="panel-heading">
<h4 class="panel-title">
<a data-toggle="collapse" href="#acc113">
目次１－１－３
</a>
</h4>
</div>
<div id="acc113" class="panel-collapse collapse">
<div class="panel-body">
</div>
</div>
</div>
</div>
</div>
</div>
</div>
<div class="panel panel-default">
<div class="panel-heading">
<h4 class="panel-title">
<a data-toggle="collapse" href="#acc12">
目次１－２
</a>
</h4>
</div>
<div id="acc12" class="panel-collapse collapse">
<div class="panel-body">
</div>
</div>
</div>
<div class="panel panel-default">
<div class="panel-heading">
<h4 class="panel-title">
<a data-toggle="collapse" href="#acc13">
目次１－３
</a>
</h4>
</div>
<div id="acc13" class="panel-collapse collapse">
<div class="panel-body">
</div>
</div>
</div>
</div>
</div>
</div>
</div>
<div class="panel panel-default">
<div class="panel-heading">
<h4 class="panel-title">
<a data-toggle="collapse" href="#acc2">
目次２
</a>
</h4>
</div>
<div id="acc2" class="panel-collapse collapse">
<div class="panel-body">
</div>
</div>
</div>
<div class="panel panel-default">
<div class="panel-heading">
<h4 class="panel-title">
<a data-toggle="collapse" href="#acc3">
目次３
</a>
</h4>
</div>
<div id="acc3" class="panel-collapse collapse">
<div class="panel-body">
</div>
</div>
</div>
</div>
リストグループを折りたたみ
<ul class="list-group">
<li class="list-group-item">
<a data-toggle="collapse" href="#lg1">
目次１
</a>
<div id="lg1" class="panel-collapse collapse">
<div class="panel-body">
<ul class="list-group">
<li class="list-group-item">
<a data-toggle="collapse" href="#lg11">
目次１－１
</a>
<div id="lg11" class="panel-collapse collapse">
<div class="panel-body">
<ul class="list-group">
<li class="list-group-item">目次１－１－１</li>
<li class="list-group-item">目次１－１－２</li>
<li class="list-group-item">目次１－１－３</li>
</ul>
</div>
</div>
</li>
<li class="list-group-item">目次１－２</li>
<li class="list-group-item">目次１－３</li>
</ul>
</div>
</div>
</li>
<li class="list-group-item">目次２</li>
<li class="list-group-item">目次３</li>
<li class="list-group-item">目次４</li>
</ul>