What is the best way to have many objects (trees, etc)

If i want to put 5000 trees on my terrain mesh what would be the best approach?

Combine them all into a single mesh and ignore occlusion/lod capabilities?

Make 5000 game objects? I've experimented with making many game objects and the performance was sub-optimal so I don't really think this is a great approach.

How does the unity terrain handle trees?

Is there a way to do instancing without a game object for each instance? Like multiple meshes on the same game object?

 

Combining them into one object is not a good option, then Unity will be calculating the entire object regardless if the camera only sees a tiny part.

on the other hand, if you have a lot of objects then it might strain the performance especially with real-time lights and shadows.