I have an oak tree sapling that is about 5 years old and it is about 4 foot tall. My question is about pruning the lower branches. The tree has several branches towards the bottom of the trunk. What is a good pruning regimen to give the tree a good shape? I do realize that the lower branch pruning would be done over several years. I put a wire cage around it to stop the local critters from pruning it off at the ground.