MY VEHICLE WAS PARKED, RUNNING AND UNOCCUPIED ON THE STREET. MY WIFE ENTERED FROM THE PASSENGER SIDE REACHING IN TO RETRIEVE SOMETHING FROM THE CENTER CONSOLE. SHE PRESSED THE START/STOP ENGINE BUTTON TO SHUT OFF THE VEHICLE. THE CAR STARTED ROLLING BACKWARDS DOWN A HILL, KNOCKING MY WIFE TO THE GROUND CAUSING INJURY. CAR CONTINUED TO ROLL UNTIL IT STRUCK A TREE.