The flight was a night navigation exercise associated with the pilot-under-instruction's (PUI) training for the award of a Night Visual Meteorological Conditions rating. The pilots had completed a briefing before departure, but its content was restricted to flight planning aspects only. An enroute landing had not been planned, but the instructor decided that the PUI should carry out a touch and go landing at Narrogin when he saw that the north/south runway flare path was illuminated. The flight was the PUI's third night flying training flight and was his first away from Jandakot at night. Aircraft attitude and directional control at night is enhanced, in the Jandakot area, by the high level of ground lighting which provides a natural horizon. In areas where ground lighting is not available the pilot must rely on the information provided by the aircrafts instruments and in particular the artificial horizon. During the takeoff from Narrogin the PUI used an incorrect attitude and directional maintenance technique when he initially selected a wings level and 10 degrees nose up attitude on the artificial horizon but then attempted to maintain that attitude by holding an indicated airspeed of 75 knots without further reference to the artificial horizon. This resulted in the aircraft entering a left hand descending turn. The instructor allowed his attention to be drawn away from his pilot monitoring role by an apparently subtle engine r.p.m. fluctuation shortly after the touch and go landing, and did not detect the pilot's incorrect technique until too late. When the instructor did perceive that the aircraft was near the ground and took control, there was insufficient time to recover before the aircraft collided with a tree. The aircraft continued to fly without any obvious damage or control problems, and the instructor elected to continue to Jandakot, expecting to have landing gear problems on arrival. These did not eventuate and the aircraft landed safely at Jandakot.