VEHICLE WAS BACKED INTO GARAGE TO TOWEL DRY AFTER WASHING. VEHICLE WAS PLACED IN PARK, TURNED ENGINE OFF AND I EXITED THE VEHICLE. AFTER COLLECTING DRYING TOWELS I PROCEEDED TO LOCK VEHICLE (CONFIRMED BY BEEP) AND STARTED TO ENTER MY HOME WHEN I NOTICED VEHICLE BEGINNING TO ROLL OUT OF MY GARAGE. I COULD NOT CATCH IT BEFORE IT ROLLED DOWN MY DRIVE AND ACROSS MY STREET INTO A TREE DAMAGING FRONT END OF VEHICLE. WHEN I REACHED VEHICLE AND UNLOCKED IT TO ENTER IT WAS STILL IN PARK. I THEN STARTED VEHICLE AND BACKED IT UP (DRAGGING FRONT BUMPER) INTO MY GARAGE.