Here it’s the answer for those who are looking for a solution in Bootstrap 3(like myself).
The HTML part:
<div class="btn-group">
<button type="button" class="btn btn-danger">Action</button>
<button type="button" class="btn btn-danger" data-toggle="collapse" data-target="#demo">
<span class="glyphicon glyphicon-minus"></span>
</button>
</div>
<div id="demo" class="collapse in">Some dummy text in here.</div>
The js part:
$('.collapse').on('shown.bs.collapse', function(){
$(this).parent().find(".glyphicon-plus").removeClass("glyphicon-plus").addClass("glyphicon-minus");
}).on('hidden.bs.collapse', function(){
$(this).parent().find(".glyphicon-minus").removeClass("glyphicon-minus").addClass("glyphicon-plus");
});
Example accordion:
Bootply accordion example