Like most Pokmon cards, the value of Grand Tree depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Stellar Crown)
Unnatural Growth + Zopandrel, Hunger Dominus Doubling your creatures' power and toughness might be the best way to pump your creatures, especially if you mix in some other buffs
Equip worthy (A creature is worthy if it's a legendary non-Villain that's red and/or white.) , Discard this card: It deals 2 damage to each creature
However, for every expensive card with remarkable artwork, there's another that looks unsuspecting but costs just as much
9, 1999 Professor Oak is that card
Its not often Magic: The Gatherings story feels fully palpable in the way cards are designed