TreeView link issue

I have a TreeView that populate data from a XML file. I also have a CssClass for it.
<asp:TreeView ID="TreeView1" runat="server" DataSourceID="XmlArticle" RootNodeStyle-CssClass="rootNode" > <DataBindings>    <asp:TreeNodeBinding DataMember="Book" TextField="Title"/>    <asp:TreeNodeBinding DataMember="Chapter" TextField="Heading"/>    <asp:TreeNodeBinding DataMember="Section" TextField="Heading"/> </DataBindings>
</asp:TreeView> 
<asp:XmlDataSource ID="XmlArticle" runat="server" DataFile="~/XML/TreeArticle.xml"></asp:XmlDataSource>
<?xml version="1.0" encoding="utf-8" ?>
<Book Title="The Book">    <Chapter Heading="Chapter 1"&g ...