(2D Top Down Shooter, Unity2D) Creating a bullet trail effect?

I'm wondering how would someone create a bullet trail everytime the player shoots. What I mean by a bullet trail is that for example, a machine gun would have a medium trail behind a bullet, pistol would have a short trail and rocket/missile might have a long smokey trail behind it.

Can this be done inside Unity2D with some codes? Or do I have to animate every bullet so that it has a trail animation going on (the problem with this is, if it was a missile, the tra. would be going on a curve depending on where the enemy is).

Thanks!