It was easy to make Mega1 menu vertical with the following code

<ddr:MENU MenuStyle="Mega1" runat="server">  <ClientOptions>  <ddr:ClientString Name="ControlOrientation" Value="Vertical" />  </ClientOptions>  < /ddr:MENU>

How can I achieve a vertical menu with the Mega2DNN Menu. I tried something like this

<dnn:MENU ID="Mega2DNN" MenuStyle="Mega2DNN" runat="server">
<ClientOptions>
<dnn:ClientString Name="ControlOrientation" Value="Vertical" />
</ClientOptions>
</dnn:MENU>

but realised "ClientString" is not a known element