Beserker Treant

Dormancy. While the treant remains motionless, it recharges. May take a long rest as a bonus action, functioning identically to if a player were to.

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

Multiattack. The treant makes two slam attacks.

Lightning Bolt (Spell). A stroke of lightning forming a 100-foot-long, 5-foot-wide Line blasts out from you in a direction you choose. Each creature in the Line makes a Dexterity saving throw, taking 8d6 Lightning damage on a failed save or half as much damage on a successful one.

Slam. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 16 (3d6 + 6) bludgeoning damage.

Whip. Melee Weapon Attack: +10 to hit, range 60/180 ft., one target. Hit: 28 (4d10 + 6) bludgeoning damage.

Animate Trees (1/Day). The treant magically animates one or two trees it can see within 60 feet of it. These trees have the same statistics as a treant, except they have Intelligence and Charisma scores of 1, they can't speak, and they have only the Slam action option. An animated tree acts as an ally of the treant. The tree remains animate for 1 day or until it dies; until the treant dies or is more than 120 feet from the tree; or until the treant takes a bonus action to turn it back into an inanimate tree. The tree then takes root if possible.