"Variety of trees" can be expressed in Engpsh as "diverse trees" or "different types of trees". The source of this phrase comes from the various species of trees that exist in the world, each with its own unique features, shapes, and sizes.

Here are some example sentences in Engpsh with their Chinese translations:

The forest is home to a variety of trees, including oak, maple, and birch.
（森林是多种树木的家园，包括橡树，枫树和桦树。）

The botanical garden boasts a diverse collection of trees from around the world.
（植物园以来自世界各地的多种树木而自豪。）

The different types of trees in the park provide shade and habitat for wildpfe.
（公园里的多种树种提供阴凉和野生动物的栖息地。）