I read a book on mind maps once

Do you have a title or author? There's a good book which discusses (amongst other things) how diagrams (like trees) developed in European books: Walter J. Ong Ramus, Method, and the Decay of Dialogue: From the Art of Discourse to the Art of Reason 1953. Peter Ramus was a humanist and an education theorist in the 16th century. Anyway, I am not convinced that we know what thought or thinking is (really) and how thoughts are "mapped" out in the brain. A tree diagram like the one in the link are good at showing relationships between languages, but there was (early on) a competing map of language development to the orthodox Stammbaum theory (family tree), and it was called the Wave Theory. That languages develop over time like the waves on a pond after a pebble has been dropped in, overlapping and expanding waves of change. While we're on it, some linguists who study semantic fields (i.e., how words can be grouped together by meaning rather than form) draw diagrams similar to the one under discussion. (See the Wikipedia article on tree model.)

Ceci n'est pas un seing.