Immediately after take-off the aircraft was seen to enter a steep climbing turn to the left. After turning through about 135 deg, and at an estimated height of 100 to 150 ft agl, the aircraft suddenly pitched nose down and lost height. The aircraft collided with a tree prior to impacting the ground in a nose-low left wing down attitude. The investigation did not reveal any mechanical faults with the aircraft that could have contributed to this accident. The pilot had been flying and working long hours and had been seen to hurry his circuit procedures in the past. On this occasion adequate flying speed was not maintained for the manoeuvre being attempted. The turn after take-off was made into the late afternoon sun and it is possible that the pilot`s vision was affected by sun-glare.