Academia is not that big, is quite incestuous, and such trees or descent are not rare. I think there was a website that listed people's academic family here is one for neuroscience: https://neurotree.org/neurotree/
what do you mean by "incestuous"? I'm having a hard time picturing the tree structure. Like if we keep things simple and assume every person on the tree "asexually spawns" multiple students, where does the "incest" come in? Maybe one student having more than one advisor? If that's the case, usually it's just a thesis committee or reviewer or something, and not really multiple _main_ advisors
Having a junior and a senior advisor is fairly common. Sometimes the work is done in multiple institutions, with a separate advisor in each. In some systems, most people who supervise students are not formally qualified to do so, creating a need for a separate formal supervisor. Sometimes there are two equal advisors, and sometimes the advisor changes for various reasons. Sometimes the student is an independent scholar and the advisors are only loosely involved in the work. If you only have written records, it can be impossible to tell which of these was the case for a particular student.
