Why trees and other things are running while we sitting in a moving bus?

Trees don't run. They don't have legs.

Hi, aisanu!

Why are you asking the question, please?

Thanks!

Physically, you are still. And so are the trees in direct comparison to you. But you are being moved by an external force like a car or bus. It depends on the speed you move, and somewhat the distance you are from the trees or objects outside, but visually you are focusing on the same spot while things [trees] move through it. For example, instead of trees - you are on a moving bus looking outside with different people lined up along the road. The people are not moving. The bus you are on is passing each one by and that is what you are seeing. If you're driving fast, and trees blur together a little, it is because of the speed you're going, compared to how fast your eyes put together the image.