The same two categories are fine; the answer is when in doubt the competitor in question competes in the more competitive category.
Any birth male, regardless of transition status=male division
Birth female who is on testosterone for identity purposes=male division
As a result, any trans athlete will be very unlikely to compete at a high level of competition, but I think think this is fair. No?
Get's a little harder when addressing Semenya and similar situations. To a degree I view it as she was born female, and the additional testosterone from her condition is a part of her talent. All high levels runners have some genetic markers that differentiate them from the general populace.