to be forcefully hit, struck, decked, or smacked by any object, not necessarily a tree.
1. While taking his morning jog, Rory was treeslammed onto his ass by a rogue labrador retriever.
2. Driving strong to the basket, the skinny Japanese warrior was treeslammed back to Shanghai by a 6 foot tall, 350 lb man named Dave who shouted, "Who's your daddy" in a loud boisterous voice, consequently chest bumping several of his buddies, who in turn erupt into arrogant, ethnocentric laughter and commence hurling racial slurs in the general direction of the prostrate Japanese tool immobilized on the ground...oh, and the basket didn't go in either.