How to add notes from one staff to the notes in another staff.

I am arranging a song that originally had a separate electric bass part and a piano part. I started arranging my song with those two as separate parts. Now I realize that it will work better if I just let the piano play the piano's original part as well as the electric bass part.

Is there a way to copy the bass part into the piano's bass clef staff without wiping out the piano's original notes?

What I'm thinking is, can I copy the electric bass part and paste it into the piano's bass clef as a separate voice?

TIA