What happened
During the takeoff roll, the pilot-in-command noted that the aircraft pitched to the left with greater intensity than previous operations. The pilot did not abort the takeoff, instead attempting to correct the deviation using right rudder and right brake.
As the aircraft returned to the center of the runway, the pilot continued to apply power and released pressure from the right brake. Upon releasing the right brake, the aircraft pitched sharply to the left toward a group of small trees. The pilot applied hard left rudder to avoid a head-on collision as the aircraft began to ground loop, but the aircraft ultimately impacted a tree on its right side and came to a stop.
Prior to the event, the pilot had not warned the rear seat passenger that their feet could contact the brake pedals located under the seat. The pilot believed the passenger may have been resting a foot against the left brake pedal without realizing it.