二维树，实现一个三维的树林空间，优点可以减小程序的体积。能实现三维的效果，它把二维树的正面始终对着视点，从而可见的总是一棵树，而不会出现失真-two-dimensional tree, to achieve a three-dimensional space woods advantage of the procedure can reduce the volume. To achieve the 3-D effect, two-dimensional tree always facing th