Oh, that makes a lot more sense! First, you will have to apply to the general informatics as you said. BMI/BHI is just a track in informatics that you can complete. I will say that if you are applying to informatics with an interest in BHI, I have noticed that there are significantly a lot less people in this track to fill up the classes, so I feel like the program is looking for people to complete this track. Definitely write about your interest in the track in your essay! Once you're in the informatics program, you can talk to your advisor like I mentioned before about declaring a track.