Trees are not as 'sound asleep' as you may think. High-precision three-dimensional surveying of 21 different species of trees has revealed a yet unknown cycle of subtle canopy movement during the night. The 'sleep cycles' differed from one species to another. Detection of anomalies in overnight movement could become a future diagnostic tool to reveal stress or disease in crops. Source 6p.
I have to agree with KNtoran. I believe that even the evergreens have a sleep cycle as well for I have seen dropped needles and "Fruit" on the ground. Each tree is unique in its own way and has a different cycle it goes through to remove old growth and make way for the new. Most humans only see this from the outside and dislike what it does to our lawns. Even though I feel the fallen leaves are Natures blanket to protect the ground for the coming winter months.