How to open submenu just by going over the menu?

I have the following Menu in css:

<div class="collapse navbar-collapse"> 
    <ul class="nav navbar-nav navbar-right"> 
        <li class="scroll <? if(!$this->uri->segment(1)) echo "active"; ?>"><a href="<? echo base_url(); ?>">Home</a></li> 
        <li class="scroll <? if($this->uri->segment(1)=='empresa') echo "active"; ?>"><a href="<? echo base_url("empresa/detalhes/1/sobre-a-nuclemig"); ?>">Institucional</a></li> 
        <li class="scroll <? if($this->uri->segment(1)=='curso') echo "active"; ?>"><a href="<? echo base_url("curso"); ?>">Cursos</a></li> 
        <li class="scroll <? if($this->uri->segment(1)=='unidade') echo "active"; ?>"><a href="<? echo base_url("unidade"); ?>">Unidades</a></li> 
        <li class="scroll"><a style="cursor:pointer" id="manual-ajax">Quero Desconto</a></li> 
        <li class="scroll <? if($this->uri->segment(1)=='vantagem') echo "active"; ?>"><a href="<? echo base_url("vantagem"); ?>">Vantagens Exclusivas</a>
          <ul>
            <li class="scroll"><a href="">Design</a><li>
            <li class="scroll"><a href="">Development</a><li>
            <li class="scroll"><a href="">Marketing</a><li>
          </ul>                     
        </li> 
        <li class="scroll <? if($this->uri->segment(1)=='depoimento') echo "active"; ?>"><a href="<? echo base_url("depoimento"); ?>">Depoimentos</a></li> 
        <li class="scroll <? if($this->uri->segment(1)=='faleconosco') echo "active"; ?>"><a href="<? echo base_url("faleconosco"); ?>">Fale Conosco</a></li> 
    </ul> 
</div> 

I need to move the mouse to advantage, for example, go down the submenu, how can I do this? I'm using the normal bootstrap class to manage the menu.