How often we need to water trees depends on a few things. Recently transplanted trees need to be watered more often than established trees, because their root systems haven’t yet grown out of the restricted form they had in the nursery pot. Water these trees a few times a week.
Dormant trees should be watered about once per month, so they don’t start the growing season already needing water.
Trees in small soil volumes need watering more often than trees with unrestricted soil volume (assuming the latter is watered across the whole available soil surface).
Trees in a sandy soil will need watering more often, but with less water. Trees in a clay soil will need watering less often, but with more water.