The gravitational pull of the earth causes any object to fall to the ground.

If it were not for the gravity, the ornaments you currently find on the floor would be on the ceiling.

If your tree was outside, those same ornaments would be in a low earth orbit, possible colliding with the telecommuncation satellites currently in place. You would be responsible for any damage caused to that hardware.

OR

It could be that the tree is playing fetch with the cat.