Unable to click on element in selenium webdriver -

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i working on project, need click on split button (arrow head).

below html:

<table id="ext-comp-1006" cellspacing="0" class="x-btn support-servicedesk-sb casemru standardobject mruicon support-servicedesk-sbactive x-btn-noicon" style="width: 250px; height: 26px;">     <tbody class="x-btn-small x-btn-icon-small-left">       <tr>          <td class="x-btn-tl">            <i>&nbsp;</i>            </td>          <td class="x-btn-tc"></td>      <td class="x-btn-tr">         <i>&nbsp;</i>       </td>       </tr>      <tr>        <td class="x-btn-ml">            <i>&nbsp;</i>          </td>      <td class="x-btn-mc">        <em class="x-btn-split" unselectable="on" id="ext-gen100">        <button type="button" id="ext-gen33" class=" x-btn-text">           <div class="mruicon"></div>           <span>cases</span>      </button>     </em>  </td>     <td class="x-btn-mr">       <i>&nbsp;</i>    </td>  </tr>   <tr>      <td class="x-btn-bl">          <i>&nbsp;</i>  </td>     <td class="x-btn-bc"></td>  <td class="x-btn-br">     <i>&nbsp;</i>  </td>  </tr>  </tbody>  </table>

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my code click on split button:

driver.findelement(by.classname("x-btn-split")).click(); 

i tried id throwing couldn't find element error.

try one:

driver.findelement(by.xpath('//button[@id="ext-gen33"]')).click()