The hedgehogs made a lot of yen in their tree business. They'd yell "GET YOUR trees here, cheap!"
残 (remain behind) + 業 (business)
= 残業 (overtime work)
産 (childbirth, production of things) + 業 (business)
= 産業 (heavy industry)
industry, like 'the steel or construction industry.'
工 (craft or industry) + 業 (business)
= 工業 (industry)
the fishing industry