False Appearance. While the Gargantuan treant remains motionless, it is indistinguishable from a normal tree.

Forest Tactics. The Gargantuan treant has advantage on attack rolls against a creature if at least one allied plant is within 5 feet of the creature and the allied isn't incapacitated

Siege Monster. The treant deals double damage to objects and structures.

Multiattack. The treant makes two slam attacks.

Slam. Melee Weapon Attack: +12 to hit, reach 5 ft., one target. Hit: 27 (6d6 + 6) bludgeoning damage.

Rock. Ranged Weapon Attack: +12 to hit, range 60/180 ft., one target. Hit: 50 (8d10 + 6) bludgeoning damage.

Animate Trees (1/Day). The Gargantuan treant magically animates one or two trees it can see within 60 feet of it. These trees have the same statistics and abilties as a treant. An animated tree acts as an ally of the Gargantuan treant. The tree remains animate for 1 day or until it dies; until the Gargantuan treant dies or is more than 120 feet from the tree; or until the Gargantuan treant takes a bonus action to turn it back into an inanimate tree. The tree then takes root if possible.