You take an action to hold up a piece of a dragon, as a wooden facsimile builds itself up at a point you can see within 60 feet of you. The construct uses the same stat block as an Adult Brass Dragon with several changes.

The Wooden Dragon only has 100 health, which cannot be recovered by another creature healing it. It changes its immunity to Fire to a vulnerability, but gains resistance to Acid, Poison and nonmagical Piercing/Bludgeoning/Slashing damage. It is also not considered a Dragon creature but a Plant, and loses both Frightful Presence, Legendary Actions and Resistance and its Fire Breath. However, it gains a new attack action, as detailed below.

Nature's Hold. The dragon shoots wooden tendrils out towards a Medium or smaller target up to 20 feet away from it. The target has to make a DC 15 Strength save or be considered grappled by the Wooden Dragon. At the end of each of its turns, the Wooden Dragon can have the target make a DC 19 Con save and take 3d6 Poison damage and 4d6 Bludgeoning on a failed save, or half as much damage on a successful one, as the tendrils slowly crush the target and release a toxic gas from within. The tendrils can be broken if enough damage has been taken. They have an AC of 16, and 20 hit points, and are resistant to all Bludgeoning damage, but are vulnerable to Fire and magical Slashing damage. If the target is reduced to 0 hit points by this attack, the Wooden Dragon restores the damage they dealt as hit points. The Wooden Dragon can have up to three creatures grappled at once. 

To use it, the caster must use their action to have it move, and/or attack twice with its tail, claw, bite, or grapple attacks. If the surrounding area is a forest, the caster can use their Bonus Action to trigger the Lair Effect of an Adult Green Dragon. 

If the caster ever moves beyond 120 feet of the Wooden Dragon, or loses concentration on the spell, the Wooden Dragon falls to pieces and cannot be put back together unless the spell is cast again.