The pilot reported that during the landing roll on a dirt airstrip the airplane approached "the second part of the runway that is at a slight angle and incline" to the first part of the strip. He stated that as he began slowing the airplane, the right wingtip stuck a tree located adjacent to the runway and the airplane immediately yawed 90-degrees to the right. The airplane exited the runway surface area, traveled down a small embankment, and impacted a group of small trees, which resulted in structural damage to both wings and engine firewall. The pilot reported that there were no mechanical malfunctions with the airplane during the accident sequence.