VEHICLE WAS PARKED ON A SLIGHT INCLINE AND ENGINE WAS OFF. PARKING BRAKE WAS ENGAGED. I OPENED THE PASSENGER DOOR TO GET MY BAG OUT AND REACHED OVER TO REMOVE MY KEYS FROM THE IGNITION. MY ARM BUMPED THE GEAR SHIFT AND THE CAR BEGAN TO ROLL BACKWARDS. I TRIED TO MOVE IT BACK IN PARK BECAUSE MY 18 MONTH OLD DAUGHTER WAS IN THE BACK SEAT (IN HER CAR SEAT) BUT I COULDN'T MOVE THE SHIFTER AND THE TIRE RAN OVER THE RIGHT SIDE OF MY BODY. THE CAR RAN INTO A TREE AND BENT THE PASSENGER DOOR OPEN TO THE FRONT FENDER. WE MOVED THE CAR BACK TO THE DRIVEWAY AND RECREATED THE EVENT. THE SHIFTER MOVES EASILY OUT OF PARK WITHOUT NEEDING TO ENGAGE THE BUTTON; EVEN WITH THE EMERGENCY BRAKE ENGAGED.