When the world tree nears its end a seed will fall off and it will start to grow and become a sentient tree with arms and legs which will continue to grow with age until it becomes the next world tree, but this process takes over 1000 years to complete and this is the cycle of the world trees.
ability score increase:Your Wisdom increases by 2. Your Strength increases by 1
age: 1000+
alignment: Good
Size: Gargantuan
speed: 30
Languages: Common, Sylvan
race features:
Tree Form: you can transform into a tree, the size of the tree will depend on your current age (10ft per 10 years)
Photosynthesis: During a short or long rest, if you spend at least 1 hour in direct sunlight, you regain hit points equal to your level. This ability can be used once per long rest.
Natural Armor: Your bark-like skin provides you with protection. Your AC is 13 + your Dexterity modifier when you aren't wearing armour. You can use a shield and still gain this benefit.
Deep Roots: As you age, you draw more power from the earth. Choose one of the following abilities based on your age:
Sapling (up to 100 years old): You have an advantage on saving throws against being knocked prone.
Mature Tree (100-500 years old): You gain proficiency in the Athletics skill and can take the root action as a bonus action.
Ancient Grove (over 500 years old): Your Strength score increases by 2 (maximum of 22), and you have an advantage on saving throws against being restrained or grappled.
Rooted (Action): As an action, you can plant your feet into the ground, becoming immobile. While rooted, your movement speed becomes 0, but you gain temporary hit points equal to your level plus your Constitution modifier, and you have advantage on Strength checks and saving throws. These benefits last for 1 minute, or until you end this effect as a bonus action. Once you use this feature, you can’t use it again until you finish a long rest.