A photo would help maybe.....have you watered the tree after planting as it will drop its leaves to reduce water loss.

Sometimes the root ball stays as a solid block. If it's dry and hot, as it is here at the moment. Try a trickle from the hose overnight. Cut the base off a couple of 2 litre plastic bottles and put them about 8 inches neck down in the soil about a foot away from the tree slanted slightly towards the tree and water through them as well. One of my pears did this when new planted. I rescued it and made a fuss of it. There is a good crop this year. By the way, if you only have one apple, and none nearbye you may need another variety as a pollinator. You can google this if you know the name of your apple tree

No leaves on the ground at all? Do you have someone helping you to garden, who may have cleaned up the mess? Or did you have hard winds that may have blown all the leaves away? Or, are the twigs cut off cleanly, as if with pruning shears? That last may mean that some grazing animal has got at it, if any are in the neighborhood.