It is just the same three recurring daily packs that are there every single day, similar to "Try Your Luck."
They aren't individual packs for Great Tree event nor do they drop from the packs. It is simply buy a pack- get a dew drop. So if you already spend during events the first pack is always worth, even when no great tree is there, and the second is a net positive during tree too. If you're a big spender then, chances are, you either don't mind picking up the third pack regardless. If you're just going for the bare minimum it is not worth it as the chance for the coupon return to make it net positive isn't enough to be reliable.
Lastly if you are low spending or F2P then this obviously isn't an option and doesn't apply to you buuut at least the info is here.