The tree creatures, or treatures, are giant intelligent talking trees with fully developed consciousness and emotions. They lack the ability to walk, forever remaining where their roots are, but can determine in which direction they grow, which will in most cases be the direction in which the significant other is. However, they can also make their branches and roots grow or move rapidly.
They only mate once in their lives, in a ritual known commonly as "Screwing", and once they've done that, their genitalia remain merged forever. Since their mating is such a rare and also obscure event, people organize an event called "Treegasm" every time that is about to happen and celebrate around the treatures.
Treatures don't have much of a choice in terms of their mating partner, since their ability to move is extremely limited. Treatures will mostly always settle for the next treature in range.