To grow a God Tree, the Ten-Tails had to serve as its seedling. This was fundamentally different from simply planting a tree; it was not just a matter of watering roots buried in the soil. Cultivating the Ten-Tails into a God Tree required one special condition to be met: the Ten-Tails had to devour an Ōtsutsuki!
Only this method could turn the Ten-Tails into a God Tree. This was also why the Ōtsutsuki Clan attacked planets in pairs. One sacrificed themselves to the Ten-Tails so the God Tree could grow, while the other guarded it until the Chakra Fruit ripened.
The one who served as the sacrifice then reincarnated through Kāma and came back to life. And thus, a world where only Mother Earth suffered was complete!
In the Samsara Grotto, Madara formed a hand seal with two fingers, and the Gate of the Great God pinning the Ten-Tails' head rose!
"Roaaar...!" The Ten-Tails immediately let out a ferocious roar, the eye on its forehead fixed on the dying Isshiki lying on the ground!
"Easy, Ten-Tails. You're about to have quite a feast..."
As Naruto raised his hand, Isshiki floated toward that gaping maw.
"..." In his final moments, Isshiki regained consciousness. His hollow eyes turned toward Naruto, looking particularly horrifying. Belatedly, he realized, "I see. Naruto Uzumaki, so this is what you're planning. But I'm afraid you're going to be disappointed..."
Indeed, turning the Ten-Tails into a God Tree was merely a prerequisite for harvesting fruit. In reality, a God Tree might bear a Chakra Fruit, or it might not. Just like apples and oranges, a good fruit tree produced good fruit, and a good God Tree produced a good Chakra Fruit.
A young, healthy Ōtsutsuki made better food for the Ten-Tails than an unhealthy one on the verge