The GitHub "network graph" is most known for exploring fork activity, but even in a single repo scenario with no forks you can still use it as a cudgel to show

The GitHub "network graph" is most known for exploring fork activity, but even in a single repo scenario with no forks you can still use it as a cudgel to show some idea of the complex graph if you need to stick with GitHub provided visualization tools. (It doesn't help that several UX redesigns have done nothing but bury the network graph, but it's still around.) You might think about investing in a copy of a client that puts the graph up front for that developer, such as GitKraken. Though I've actually had good success with a tool that is free and already out of the box in most git installs: gitk. gitk is ugly, but it gets the idea across and is easier to teach most developers to use than trying to get them to remember to add the --graph flag to git log. (Though adding a good alias for `git log --graph` or some further relative like `git log --graph --oneline` and encouraging them to use the alias instead is also another option.)