Redwood Trees are trees that naturally spawn in Redwood Forests. Like real redwoods, they are very tall, very wide and can be harvested for a large amount of wood.
Redwood saplings require a lot of empty space around them to grow into trees. The smallest area required is one sapling in the middle of a 9x9 square. Saplings can mature into full grown trees above y=60 in Version 1.10.2.
Version 1.2.0+ - As of version 1.2.0, only one Redwood sapling is required to grow a tree.
Before version 1.2.0 - To spawn a redwood, the nine saplings must be planted in a 3 by 3 square. They must be planted on grass blocks, not dirt, and must have one extra block on each side, illustrated by the yellow blocks. The red blocks being where the saplings are planted.