[Mz]

Some people cannot see the trees for the forest. Others cannot see the forest for the trees. If you do not understand that they are both true and real and right there in front of you, you have missed something important somewhere along the way.

[xpinguin]

Actually, only tree is real. "Forest" is a mental construction - just region of space with the density of trees being high enough. Play with that "high enough" variable, and a meaning of "forest" will drift.

[mc808]

"Tree" is also a mental construction. It is just a bunch of particles that form a recognizable pattern in the features and scale we've evolved to discern in the world. Examine two trees in enough detail, and the vast differences may make the tree-scale similarity seem utterly insignificant. But alas, "particle" is also just a mental construction...