There is a secondary interesting thing on this image (and it might not be the intention of the author). The representation of d, e and f in the indented list and the tree map, is not consistent. For the indented list there "must" be 3 bullets, and in the tree map the box "must" be arranged horizontally instead of vertically. I say "must" if one wants to stay consistent, but it can be a visualisation choice to do it that way to be more expressive (according you have "measured" it is actually more expressive).