Git in layman's terms: isomorphic contours in source-code phase space
tartley.com
tartley.com
Also, a tree of trees is still a tree. Git repositories form DAGs of trees, and this is not really that hard to visualize.
It is also a bit funny because a lot of educated readers will try to make sense of the explanation, but the explanation is utter nonsense and has nothing to do with how Git works.
It's definitely not complete but gets them to appreciate it.