Hey! I understand the confusion, as that is a VERY common misconception from people outside of the bisexual community!!
Of course, no bisexual is going to experience attraction in the same way another does. So, you may meet bisexuals who are only attracted to cis men/women, but not trans* men/women. This is not to speak for the bisexual community as a whole, though! It is simply a matter of personal preference.
Having said that, it is widely accepted by the bisexual community that bisexual does NOT mean an attraction to TWO genders, but rather an attraction to genders that are the same as AND different than your own. To put it differently, an attraction to two OR MORE genders.
Yes, I could identify as pansexual and be correct. The definition of pansexual does apply to my sexual attractions. But, so does bisexual. At the end of the day, while they are not the same, bisexuality and pansexuality have a large amount of overlap. This means that members of those communities often have equal choice in what word they wish to use to identify themselves.
For me, bisexual has always felt right. While misconceptions about it can be frustrating and might be solved using the title of pansexual, that word has never felt right in identifying myself.
I hope that clears up your question. I have no problem clarifying or answering any other ones if need be.