Trees that are established are pretty good at taking in the proper amount of water it needs to survive.
When a tree gets enough water it will usually stop soaking up anymore water through the roots.
However when you're planting a tree then over watering it could cause problems before it matures but once the tree gets established and matures it will take in enough water and not drown itself.
Because when it rains the excess water soaks into the soil and the tree drinks just enough water to stay alive and grow.