If the window mode is set to Cascade, there will be three ways for arranging the windows: Tile Vertically, Tile Horizontally, and Cascade.
Instructions
The Tile Horizontal, Tile Vertical and Cascade buttons in the Windows group are only active if you choose to arrange the windows in Cascade mode.
Click either Tile Vertically, Tile Horizontally, or Cascade to arrange windows in the corresponding mode.