How do I make a object with physics behavior stop falling through stuff?

Hi, in my game I'm the making the character can cut trees, the problem is I want to make the top of the tree fall to the ground like IRL.

Hi, in my game I'm making be able character be able to cut trees, the problem is I want to make the top of the tree fall to the ground like IRL.

XD sry bout all that I've got it figured out thnx.