Forum:Categories levels

I noticed that most of articles (if not any articles) are placed both in high-level and low-level categories. I've never seen that on any wiki. I think, articles should be placed only in lowest level category. For example, articles about canceled CoD4 singleplayer levels were (were but not are because I fixed something) placed in categories like shown on my table (the categories that articles included in are marked with green color):

I think an article about CoD4 singleplayer cancelled level should be only in Call of Duty 4 Cancelled Levels, because it's lowest level category. This will look like in table below:

Or even like in following table:

Categories are trees. Apple can't grow on trunk, but can grow on branch.

Discuss.