Once you do this, you have the chord symbols and Melody, and you can select a style that you want to use to create an accompaniment. Band-in-a-Box ® will interpret the chords from your MIDI file and write these in the Chord Sheet window, and will also import one or more instruments (usually the Melody and Solo) to the Melody and/or Soloist tracks.
You can use File | Import Chords from MIDI. Band-in-a-Box ® will import the MIDI file into the Melody track, convert the Melody track to a multi-channel track so that it can play more than one instrument, and automatically disable the style (accompaniment). Starting with Band-in-a-Box ® 2004, you can import and play an entire MIDI file by using File | Open MIDI file(F7). Band-in-a-Box ® is mainly intended to be used as an intelligent arranger and the ways that you normally use MIDI files with Band-in-a-Box ® reflect this.
If your goal is to import a MIDI file and view/edit each instrument on a separate track in its original form, you would be better off using PowerTracks Pro Audio. However, Band-in-a-Box ® isn't a dedicated MIDI file sequencer. Yes, Band-in-a-Box ® will import and play entire MIDI files, and there are a number of other ways that you can use MIDI files with Band-in-a-Box ®. Can I import and play MIDI files with Band-in-a-Box ®?