The Mangrove Tree can be found growing in clusters throughout the mangrove biome. They have bright white wood and planks.
Raw wood: Mangrove wood
Planks: Mangrove planks
Crafting: Slabs, Stairs, Fences, Fence Gates, Doors
Mangrove saplings can only be grown on sand in older versions. When a sapling grows, it produces a "root structure" made of mangrove wood which extends several blocks into the ground and will destroy any block, including bedrock, in its path. In newer versions, you use bonemeal in the centre of a 3x3 patch of Mangrove saplings, but you may want to put the saplings one or two blocks lower if you want a shorter tree.
Do not plant mangroves near anything you do not want to lose. It won't destroy the contents of a chest, but it will break the chest and the items may despawn on the ground.