Most Git commits (almost all non-merge commits) only point to one other commit (node, whatever) and that still forms a tree of branches naturally. Rebase is a "consensus algorithm" that some need in git to keep their commits a straight line. On a single machine a blockchain consensus algorithm is nearly indistinguishable from "rebase" and yeah doesn't "feel like you need a consensus algorithm". That doesn't mean there isn't a consensus algorithm.

Multiple different heads is a tree. Multiple forks is very much a tree. I think it is Blockchain proponents that are overcomplicating things and bending over backwards to describe their Merkle trees as non-tree as possible.