On Lutum when someone dies, they are often buried with a tree seed in their mouth. The species of tree doesn't entirely matter, although many families prefer to use the same species for themselves.
This is done to give the dead a peaceful afterlife before their souls leave entirely. One life among the people and one life among trees.
Once a burial tree dies, it is believed that the soul has departed into the unknown. The length of time a tree remains is thought to be the time that the dead stay to look over their friends and family, where some may leave immediately when the burial tree does not sprout, and some may stay for hundreds of years and go on to support the entire forest.

Burial forests can be found all over the planet, though most are in the Deepmuds region. This also serves as a lesson to the living that trees should be respected since they were all once people and animals (also so you don't accidentally piss off an entire family by desecrating their burial forest).
Curiously, though the trees of Lutum have a vastly different way of reproduction from people, certain morphs of specific trees tend to line up with the gender of the person it sprouted from with no relation to sex (the trees support trans rights >:3). It makes up pretty hard evidence that the soul of the person is transferred into the tree, although it is still a mystery to the scientific community how this occurs.

Despite all this, wood is still used in construction on Lutum. Only dead trees are used though and usually are strictly for building supports, and art. Mud is the primary material in building (at least outside of the cities where stone and metal are the primary).
Each mud house is supported by 3 logs in total, so that the people's ancestors can remain and support the family even after they have departed. Logs are often carved with the face of the person they once were. In some families once the oldest burial tree finally falls, they often don't remember the face or even name of who they were, so they will carve a newly created face into the log to represent who it was.