Did you mix any clay with the peat and compost? Planting in pure organic matter causes problems for most landscape plants, particularly if the weather turns hot and dry. You could dig up the tree and replant it, but the recovery rate is pretty low.

I think this may be draught? Even if you think it has has enough water? I dont use peat as its hard to get wet once dry? ( didnt know you could still buy it?) Try really watering it and fingers crossed it may well recover next spring. I planted one last year and one this year both in heavy clay and the amount of water I have had to give this years tree because of the draught has been a lot and nearly every day.

It will take a lot more water than a pitcher or two.

If this is the problem? it is possible the tree is losing its leaves to conserve its energy and with watering will survive. In todays news its been announced that we will not have much of an autumn colour wise - because the trees are losing their leaves early due to draught. This happened to my Rowan tree last year and this year it is better than ever though I have watered it