as far as I know from trees you get treasure cards, which can only be used once. If you have a recipe for a tc then you gather ingredients and then create a tc, but once you use it it's gone you have to re-gather ingredients and create a new one :)
Actually there are permanent spells you may craft such as loremaster, deer knight, luminous weaver, lord of night, etc. its just that they are very hard to craft. You may also craft treasure cards, they are easier to make but you may only use it once.