As I understood it, the "ashes" you receive post-cremation are actually the ground remains of bones from all cremations that took place that day, and thus you can't actually guarantee that it's "you" in the urn (or the tree), it's actually just a large collection of the people cremated that day.

Apart from that, I love this idea. It actually throws up all sorts of strange meta-physical questions about the self and who we really are.

Also, for added creepiness, could you be turned into, say, an orange grove? If you were, would the people eating the fruit be somehow digesting ... you? Strange.