Pretty much dittoing Scott's advice.
I am not sure if there is a hard and fast rule for the amount of watering a new tree needs. You don’t want the soil around the roots to dry out, but equally important, you don’t want to drown them either. My guess is that a gallon or two every 2 to 3 days would be plenty assuming the ground is fairly porous, especially if you can put some sort of mulch around your new tree. The only variable is how well drained you soil is to start with… very well drained (sandy), increases watering, poorly drained (clay) reduce watering. Keep an eye on the leaves and if they start to wilt, you know you need to water more. Just my two cents.
Veering slightly off topic. If you have not yet planted your bare root tree one suggestion is to add water AS you re-fill the whole with dirt. After you add 6” or so of soil, pour in plenty of water to create a slurry of mud, then kinda jiggle the roots around which will get rid of a lot of the air pockets and give good soil contact with your small roots. Add more soil and repeat until the whole is filled. It is not the end of the world if you don’t do this, but I think it helps. Good luck, and keep us posted.
