This is really an excellent idea. This lets the departed contribute one last time to the environment and the world around them in a deeply significant way. It is a profoundly meaningful gesture both by the dead and the family. The family could also be inspired to contribute in other ways that aid the environment after having taken part in planting this tree. The act of nurturing the tree and seeing it grow through generations would definitely have a positive impact on the way that younger members of the family view sustainability and green culture. Very nice!