Why did I have to plant the tree outside the bubble?
A tree can still be alive and thriving inside a time bubble (Nature doesn't care about such details), but without the passage of time it will never grow. You could have planted the tree inside the bubble for decorative purposes, but for it to grow into a convenient natural ladder you had to go as far back as possible outside the bubble so that it would have time to be fully grown in your bubble later. You know the saying, the best time to plant a tree is a few centuries ago.