From what I have learned these are the immature leaves or they leaves of an immature plant. As the plant/tree grows the leaves will take on a more recognizable form. For the tree near my house, the landscapers are forever cutting it back to the fence line, so it may never show its true leaf shape. My plan is to find a way to get some cuttings and allow the tree to grow just long enough to document the change in leaf shape. That's the plan anyway.
Plantrob, is there any way you can hold off digging up the tree to help get a more positive identification? There should be no danger of the plant spreading if you stop the growth before the tree fruits.