http://www.jeasyui.com/documentation/tree.php是要这样一个个去拼字符串吗?   看起来很烦啊
<ul id="tt" class="easyui-tree">  
    <li>  
        <span>Folder</span>  
        <ul>  
            <li>  
                <span>Sub Folder 1</span>  
                <ul>  
                    <li>  
                        <span><a href="#">File 11</a></span>  
                    </li>  
                    <li>  
                        <span>File 12</span>  
                    </li>  
                    <li>  
                        <span>File 13</span>  
                    </li>  
                </ul>  
            </li>  
            <li>  
                <span>File 2</span>  
            </li>  
            <li>  
                <span>File 3</span>  
            </li>  
        </ul>  
    </li>  
    <li>  
        <span>File21</span>  
    </li>  
</ul>