Cut wrapping paper so you have length enough to wrap 1.5 times around. On the side leave a bit more than half height.

Fold roughly 1cm in at the edge

Fold the sides to mid point so they form a triangular shape to look like the envelope

Now wrap in from the other side. Make sure the whole top surface is covered. Tape to fix

Now fold in the envelope cover. Tape to fix

Fold in on the sides

Fix with tape

Turn to the other side and do the same

Fix with tape

and there, you have an envelope looking gift wrap! (Of course works better with a real envelop and hand written card😉)