So here's the thing.
Rabid basically covered it but here is what I say
If for example you are a trans woman and like men, then you are straight. If you are a trans woman and like women, then you are lesbian. If you are a trans woman and like both men and women THEN you are bi.
If you are talking about being non-binary, then here's that:
If you are neither gender and like men, you are kind of both gay and straight, I guess. But that is still only one gender, so that means that you would technically not be bi in that situation.
Hope that answers your question