How are treemaps hierarchical? According to various sources on the internet, treemaps are a way to visualize hierarchical, tree-like data structures, for example the tree generated by hierarchical clustering.
I looked at a lot of treemaps and I just cannot seem to understand where/how the sense of hierarchy/nestedness is conveyed. It just seems to be tiles arranged next to each other. How do I know which tile is a parent/child of which other tile(s)?
Treemaps are not very intuitive when trying to understand hierarchy levels. Sunburn chats are better.

First hierarchy level is either shown by borders or different colors.
Subsequent hierarchy level is represented by smaller rectangle which is part of bigger rectangle.

Refer this article