Meaning: This sentence is describing the mystery of trees. It is saying that the trees are tall and upright, their leaves are making a soft sound as they move in the wind, and they have secrets that they are keeping.
Choice of Words: The words "trees stand tall" are used to describe the way trees grow high and upright. "Leaves rustling" means that the leaves of the trees are making a soft sound as they move in the wind. "Secrets held" indicates that the trees have secrets that they are keeping.