How to create a dropdown menu in ASP.NET 4.5

I am trying to create a dropdown menu

This is what I have:

 <asp:Menu id="NavigationMenu" runat="server" Orientation="Horizontal" BorderColor="Black" BorderStyle="Solid" BorderWidth="1px" DynamicHorizontalOffset="16" Font-Names="Arial,Gill,Sans" Font-Size="12px" Height="32px" PathSeparator="," StaticDisplayLevels="2" StaticSubMenuIndent="2px" Width="545px">
               
<Items>
          <asp:MenuItem NavigateUrl="~/Default1.aspx" Text="Home" Value="Home"></asp:MenuItem>
                           
          <asp:MenuItem NavigateUrl="~/AboutUs1.aspx" Text="About Us" Value="About Us">
                               
                  <asp:MenuItem NavigateUrl="~/AboutUs1Sub.aspx" Text="About Us Sub"
                                    Value="About Us Sub">
                  </asp:MenuItem>
                           
          </asp:MenuItem>
  </Items>
                       
</asp:Menu>

I would like for About Us Sub to appear as a choice below About Us when About Us is clicked.

What do I need to change?

Thanks,