You can use shape cut outs as masks to create unconventional data charts. Here is how I created the pyramid-shaped stacked column chart:
  1. Insert a standard stacked column chart
  2. Cut away clutter until you are left with one huge column
  3. Insert a rectangle and a triangle
  4. Align the two shapes, select the rectangle first, the triangle second, right click, grouping, and hit subtract (PowerPoint 2011 for Mac)
  5. Color the remaining mask in the background color and position it over the graph