How to switch ribbon tab programmatically?

I have a ribbon in my view named 'ribbon' that have 2 tabs as below sample codes. I want Button1 when clicked will open Tab2 and vice versa. How would I do this?

<ribbon:Ribbon x:Name="ribbon" HelpPaneContent="{x:Static data:WordModel.Help}">
    <ribbon:RibbonTab Header="Tab1" ... >
        <ribbon:RibbonGroup x:Name="Button1" >
            <ribbon:RibbonButton Clicked="SwitchToTab2" />
        </ribbon:RibbonGroup>
    </ribbon:RibbonTab>

    <ribbon:RibbonTab Header="Tab2" ... >
        <ribbon:RibbonGroup x:Name="Button2" >
            <ribbon:RibbonButton Clicked="SwitchToTab1" />
        </ribbon:RibbonGroup>
    </ribbon:RibbonTab>
... 
</ribbon:Ribbon>