jQuery 树型菜单插件(Treeview)

<ul id="browser" class="filetree treeview-famfamfam">
    <li><span class="folder">Folder 1</span>
        <ul>
            <li><span class="folder">Item 1.1</span>
                <ul>
                    <li><span class="file">Item 1.1.1</span></li>
                </ul>
            </li>
            <li><span class="folder">Folder 2</span>
                <ul>
                    <li><span class="folder">Subfolder 2.1</span>
                        <ul id="folder21">
                            <li><span class="file">File 2.1.1</span></li>
                            <li><span class="file">File 2.1.2</span></li>
                        </ul>
                    </li>
                    <li><span class="folder">Subfolder 2.2</span>
                        <ul>
                            <li><span class="file">File 2.2.1</span></li>
                            <li><span class="file">File 2.2.2</span></li>
                        </ul>
                    </li>
                </ul>
            </li>
            <li class="closed"><span class="folder">Folder 3 (closed at start)</span>
                <ul>
                    <li><span class="file">File 3.1</span></li>
                </ul>
            </li>
            <li><span class="file">File 4</span></li>
        </ul>
    </li>
</ul>