We planted a snow crab apple tree about 3 weeks ago and it dried up and died. Now our replacement is dying.?

Now our replacement tree, a pear treee (doesnt get fruit, only flowers) is wilting and will probably die too. I dont think that we are overwatering. We water it when with the sprinkler when we water the gr (2x a day since it is new sod). We put good compost in the hole and even rock to help drain water. How can we save the tree?