A small hut with a glass dome, a walkable roof and a tree on each edge.

Instructions:

First, build an 8x8 square. Then remove the corners and plant the oak seedlings there. It is important that the square is only one block high! When the seedlings are fully grown you can cut the resulting trees to size. Now you should raise the wall of the house by 2-3 blocks. The roof is made of glass. Now you build a 1x1 wide column from the floor of the house up to the ceiling, so that you can reach the roof through ladders.