Combining a Trombone Part with a Piano Part in MuseScore 4 - Maintaining Left-Hand Octaves

I'm using MuseScore 4 and trying to combine a trombone part with a piano part. I want the trombone melody to be added to the piano part, with the left hand of the piano playing octaves throughout. However, when I copy and paste the trombone notes (Ctrl+C, Ctrl+V) into the piano staff, it replaces the existing piano notes.

How can I add the trombone notes to the piano staff as a separate voice (or system) without overwriting the existing piano notes? My goal is to have the piano's left hand continue to play octaves while the right hand plays the trombone melody. I've tried adding a new staff, but I'm unsure how to properly integrate the trombone melody into the existing piano part while maintaining the left-hand octave accompaniment.