If the tree(s) are not too thick or if your link is from a high point to a low point, 2.4GHz will probably suffice. But if 2.4GHz is over-crowded or the tree(s) are thick, 900MHz would be a better solution.
The following 900MHz options can pass through a single thick tree, or a small group of trees.
The lowest-cost option for a short link, to pass through trees, is LOCOM9
For long-distance links to pass through trees, use NanoBridge M9Author: George Hardesty