This is an exaggeration. It describes how tall and strong the Amorite people were and compares them to the tallest and strongest trees in that region. Alternate translation: "who were tall and strong like great trees" (See: [[rc://en/ta/man/translate/figs-hyperbole]] and [[rc://en/ta/man/translate/figs-simile]])
How Yahweh completely destroyed the Amorites is pictured as a tree being destroyed from top to bottom. Alternate translation: "Yet I destroyed them completely" (See: [[rc://en/ta/man/translate/figs-idiom]] and [[rc://en/ta/man/translate/figs-merism]])