Can anyone help identify this "tree?" I am having a hard time figuring it out. It is extremely aggressive Sprouts new trees from its root system. So it is coming up everywhere. The trunks dont seem to get much thicker - just grows taller (almost like bamboo). There are now around 40 of them growing in this location - some 15' tall. Long pointy leaves. Grows well in very wet conditions (growing here next to a creek).