How do you play a tremolo attached to a stack of notes on a piano?

1. How do you notate a tremolo between two notes?
2. What is a tremolo between two notes?

How do you notate a tremolo between two notes?

Tremolo

1. A one-note or one-chord tremolo is indicated by strokes through the stem of the note or chord (or above/below if a whole note). E.g.
2. In a two-note or two-chord tremolo, bars are drawn between the notes. E.g.

What is a tremolo between two notes?

Tremolos are thick, slanted lines that cross individual stems or are positioned between multiple stems. They are used to indicate that notes are repeated, either individually or in sequences of multiple notes.