I want to show the first element of this collapsible accordion. I did some research in internet but in vain
I don't think you've got all the HTML you need for the accordion to work unless you haven't pasted it all above.
The Bootstrap docs first example has the first element set to be open:
http://twitter.github.com/bootstrap/javascript.html#collapse (These docs are for v2.3.2, which is no longer officially supported.)
I think it's the class "in" that sets it to be open initially.
<div class="accordion" id="accordion2">
<div class="accordion-group">
<div class="accordion-heading">
<a class="accordion-toggle" data-toggle="collapse" data-parent="#accordion2" href="#collapseOne">
Collapsible Group Item #1
</a>
</div>
<div id="collapseOne" class="accordion-body collapse in">
<div class="accordion-inner">
Anim pariatur cliche...
</div>
</div>
</div>
<div class="accordion-group">
<div class="accordion-heading">
<a class="accordion-toggle" data-toggle="collapse" data-parent="#accordion2" href="#collapseTwo">
Collapsible Group Item #2
</a>
</div>
<div id="collapseTwo" class="accordion-body collapse">
<div class="accordion-inner">
Anim pariatur cliche...
</div>
</div>
</div>
</div>