Answer: Yes, you can overwater a new tree. If the soil remains too wet it can actually suffocate the roots because saturated soils drive out oxygen. Roots need oxygen as well as moisture. So, water deeply once each week. I wouldn't prune the branches back now - it could further stress the tree by encouraging new growth. Dead leaves and branches are dead. The tree has already sealed them off from the rest of the tree so leaving them on won't sap strength from your tree. But most importantly, what may look dead to you might not be dead at all. I would wait to see if the seemingly dead branches leaf out later this summer. If not, you can prune them off next spring. Best wishes with your new tree.
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