The tunneling between the leaf surfaces looks like damage from leaf miners which are fly, beetle or fly larvae that attack many ornamental and edible plants. Try to pick most of the infected leaves from the tree to stop the larvae from spreading. The larvae are tiny worms that tunnel into leaf tissue. They are put there by flying insects that lay eggs on the leaf surface. The larvae then fall to the ground and the life cycle repeats. You can try using sticky traps to catch adult flies and beetles or cover trees with fine netting and use a mulch on top of the soil to smother larvae. A pray of Neem oil can also help but read and follow instructions on label. Keep growing, Marianne Binetti