There are 3 components, the piano itself, the white key section and black key section. Align and glue the black key section onto the white key like so, and fits into the frontal section of the piano.

Voila:

How to print:
Printed using black PETG and white PLA, use any materials your heart desires.
Use supports for the piano body.

Shortcomings: supports up to 3 full octaves only, missing pedals, can't actually plays music.
Would looks nice sitting on a real piano.
The author marked this model as their own original creation.