Woe for the giants’ royal tree, Whose stately height was fair to see. His buds were deeds of kingly grace, His bloom the sons who decked his race. With rifled bloom and mangled bough The royal tree lies prostrate now.”

In plain words: Vibhishana compares Ravana to a tall, beautiful royal tree whose flowers were his good deeds and his sons. Now the tree lies broken on the ground.