You can control the orientation of the menu by setting its Flow
        property either to Horizontal or Vertical. The
        default value of the Flow property is Horizontal.
    
        When Flow is set, its value determines the the flow of the root
        group. If set for a particular item, it will affect the item's children.
    
        In this example, the Flow property is set in the code-behind upon
        selecting an item in the RadioButtonList on the right.