Just set your Tree up as a Zone, enter information as you wish for the zone, then make up, probably, a Fixed schedule. Use Seasonal Shift if you want it to reduce the watering in cooler weather, and set the Minutes watering time to what you calculated using the steps above. Ignore most of the other settings, which change watering time. Just set the time at the end. No sense in getting all worried with soil type and such; you know how much water you want to apply, you calculate the time you want it to water, and set it to that. Watering once a week should be fine for trees, preferred even.
