[Twisted-Python] How to bisect Twisted?

[Peter Westlake]

In the Git version of the Twisted source code, there are tags for
releases, e.g. the revision with SHA id
85a6a0f9e3c4ea22d1d72d4ca8eb0c08ee99ca85 corresponds to 8.0.0. This is
good, but there aren't any intermediate changes on that branch (tag?),
just the releases! So there isn't much for "git bisect" to work with.
I'm trying to trace a bug that wasn't in 2.5.0 but is in 8.0.0; what
arguments should I give to bisect? Apologies if this is obvious to
anyone who knows how to use git, but I'm just a beginner.

Thanks,

Peter.