Click event not fired for EasyUI Tree

When using tree module from easyUI framework, click will not fired using below method:

Html code

<li><span class="tester">TESTER01</span></li>
<li><span class="tester">TESTER02</span></li>
<li><span class="tester">TESTER03</span></li>

　　Wrong method:

$('.tester').click(function(){alert('click fired')});

　　It can be achieved by below method

$(document).ready(function() {
    $('#tester_tree').tree({
	onClick: function(node){
              alert('click fired!');
        }
    });
});