The aircraft was climbing through approximately 750 ft amsl after takeoff when it began to turn right. It continued to climb in the turn until it reached approximately 875 ft amsl when it began to descend. The descent continued until the aircraft struck some trees at the edge of a field, approximately 1.8 nm southwest of the aerodrome. The evidence available was consistent with a loss of aircraft control in Instrument Meteorological Conditions (IMC), but this could not be concluded unequivocally because of a lack of evidence from within the cockpit. However, it is possible the pilot became incapacitated and the additional crew member was unable to recover the aircraft in the height available. Three Safety Recommendations are made regarding the fitment of Terrain Awareness and Warning Systems (TAWS).