Here's the screenshot:
The problem is, with the current category selected in the image, the product will only show up in that sub-category.
I want the product to show up in all parent categories as well without having to add the parent categories to the product.
In this case, I would have to add 3 (edit: 4 more also counting the root category) more categories (all of the parent categories), just to achieve this effect.
This image below explains how it would look like when done, and the deeper the category chain the more tedious it gets to do this. It should just be a one click operation, select the sub-category and automatically have the product set on all parent categories as well.
Basically, you should just have to do this once, by selecting the sub-category and be done.
An option while creating the relation would be great.