Professor Tree is one of two residents in Beige Town, the others being Rusty and his family. He is a smoker and is almost constantly high, even trying to smuggle drugs inside of bicycles. He also seems to like Pringles.
Professor Tree bears striking resemblance to Professor Oak from the original Pokemon games, except he wears dark sunglasses to hide his eyes.
Professor Tree is always seen as high during his appearances. As such, he displays characteristics of a heavy drug smoker. He seems oblivious most of the time and sometimes shows incorrect emotions to a situation, such as laughing at Rusty buying a drug filled bike. Despite being a pokemon professor, Professor Tree knows very little about pokemon.
Professor Tree only became a professor because it was the easiest grant to acquire and he gets a monthly paycheck and a free Professor Tree's Lab and all he has to do for it is count Pidgey once in a while. The rest of his time, he reveals, is devoted to growing pot. He does not really know much about pokemon. He gives Rusty his first pokemon, a Kakuna that he thought was a paperweight. He lets Rusty go out to study Pokemon for him.
He is later seen at the Celadon Mall trying to smuggle drugs stashed inside a bike. Unfortunately, Rusty bought it by accident. Rusty later encounters Professor Tree, high once more, and his friend Nugget in an Herb Shop. They watch a Pokemon documentary, which Professor Tree and Nugget both fall asleep to.
During the Age of Doof he joins the Anti-Bidoof Resistance and becomes their top and only scientist. When sending Rusty back in time his calculations show that throwing a Magnemite into water with Dialga and Rusty should only kill one of them. This is likely to be correct, as the Dialga is not seen anywhere afterwards. When Peanut Butter finds them he "doofs" Professor Tree, who before wanted Rusty to burn the base down. He then wanders off, and is presumably alive.
- He seems to like Chicken Panini, as Rusty's Mom and Rusty's Dad ask Rusty to deliver it to him.
- Two Pidgeys in particular seem to follow Professor Tree for unknown reasons. They keep finding him by following his scent but also with help from Rusty
- His name is parody of the fact all of the professors in the Pokémon games are named after trees (e.g. Oak, Birch, etc.). Also, it is a hint to the colloquial term "tree", which is used to describe marijuana.