The whole point of bill-boarding is to use one small texture repeated constantly, with no variation between the repeats. The method is great, because it doesn't require too much graphics power, conserves size, and looks great. I'm sure (most of) you know all of Oblivion's environment is made using it. This is said to whomever does not know, because I know B2M knows
However, I do say, the texture used here is bad. I'm quite sure I've seen a weeping willow in Oblivion, and it used a larger texture that looked like a bunch of the leaf stuff clumped together like an upside down 2-d clump of grass instead of seemingly unjoined repetitive strands. And, one important lesson can be taken from Oblivion--most textures used are dark, whereas this is absurdly light. If you make the texture bright, billboarding it, as you have surely noticed, destroys what contrast you have. In any other engine, you would make the texture darker as well, but you would be able to cast some lighting effects to make it look better.
