This is a rhetorical question. It can be translated as a statement: "You can see that they are doing these bad things while the tree is green, so you can be sure that they will do worse things when the tree is dry." The meaning is "You see that they are doing bad things now in good times, so you can be sure they will do worse things in the bad times in the future." (See: [[rc://en/ta/man/translate/figs-rquestion]])
The green tree is a metaphor for something good in the present. If your language has a similar metaphor, you should use it here. (See: [[rc://en/ta/man/translate/figs-metaphor]])