。
A tree is known by its fruit.
Literal
Tree [topic-は] its fruit [by-で] is-understood.
A plainer version of the same proverb, using instrumental で instead of the formal ~によって. The same meaning, same proverb; just an everyday register. Three frames can express 'by means of X' in this kind of aphorism: the ば-conditional ('if you look at X, you understand'), the formal ~によって, and the bare instrumental で.