all of those funeral options like the tree pod or mushroom shroud or urn with seeds that "feeds" the tree are uhhhh, bullshit. unfortunately. if you want to be a tree when you die, be buried in the ground without a francy casket or embalming, and have a tree planted above you. this is the same thing as any of these hypothetical "tree pods" but it's skipping the scammy cash grab companies trying to capitalize on grief with fake ass science.
cremated remains will not "feed" anything, either. they'll probably impede growth, tbh. cremated remains are non-organic. what's left over after a cremation is hollow, dry, brittle bone fragments that someone like me sweeps up and puts in a big metal blender to create the smooth "ashes" one expects. By all means, go ahead and scatter ashes in nature, but don't expect anything to grow from them.
If you want your body to return to nature after death, go for a green burial or an at-sea burial. there are many dedicated green burial sites in the world, and one also has the option of simply being buried in a more traditional cemetery that allows for simple wicker caskets w/o a vault around them, and the body left unembalmed. If the tree thing is really your jam, go for burial in a dedicated green cemetery that allows your family to plant a sapling above you, or if it is available where you live have your body composted and use the soil to grow plants.
tldr; there are options for green funerals out there, and options for "becoming a tree," but I would not recommend going anywhere near products offering this such as tree pods, etc. as they are expensive scams preying on people's grief for their dumb start up. get composted or green buried 💚🌲 source: I'm a mortuary scientist and provider of both traditional funerals/cremations & green burial/at-sea burial.