The word "treat" generally refers to the act of giving someone something enjoyable or special, especially as a reward or as an expression of care. It can also mean to deal with a particular issue or subject in a specific way. For example, when you go out for ice cream with friends, you might say you are going to "treat" them.
The word "treat" comes from the Middle English word "tretin," which in turn comes from the Old French "traiter." The Latin root "tractare" means "to handle" or "to drag along." Over time, it evolved to encompass the idea of dealing with people or matters in various contexts.