In general leaf shape is an unimportant factor, in comparison to the actual 'oxygen/sugar factory' parts of the leaf. So different tress have evolved different

In general leaf shape is an unimportant factor, in comparison to the actual 'oxygen/sugar factory' parts of the leaf. So different tress have evolved different leaves because it's not a 'life or death' mutation. It's pretty much the same that people have evolved different hair colors which are a minor, unimportant thing in life, not like a mutation that prevents a heart from developing for instance.