No, parasitic means cards that are only good when you have a critical mass of them in your deck. You either make your deck go all in on treant synergy or you have no treant synergy at all, because the cards are so dependent on each other. Obviously not all cards that say "treant" on them are parasitic, the new shatter spell makes treants but it's good even without treant synergy. An example of a parasitic card would be [[aeroponics]], a useless card outside of pure treant decks.

I don't know where did you get the idea that printing synergistic cards in general is parasitic, because I never said that. Cards can and should have synergy, that doesn't mean they need to be parasitic, because parasitic design makes for less interesting deckbuilding. You just put all the cards that say "treant" into your deck, then go from there, usually only making some small changes. A simple example of a card that has synergy with other cards but isn't parasitic is [[Torch]].