the tree is situational, i usually plant one after i have launched my opponent and cant follow up, us ually right after i launch, gyroid to cover thier landing option.
and ive had experience with a teleporting zelda and planting trees.... not good.
i usually plant it when i can and either lure my opponent close to it or combo them across the stage to where my sapling is. that forces their hand sometimes and you can cover a lot of options. after that, at low percents, tree growth combos into up air, fair, bair, nair, or dair, and since the tree doesnt have a hurtbox where the leaves are, i lauch a gyroid to prevent jump overs, and if they do, you can respond with an up air.
when your combo heavy or in neutral, its best not to plant the sapling, but if you get them off stage, you can plant the sapling at the edge, or a little bit behind and then go off stage for the edge guard, and if they make it back, you still have the tree as a back up.
even just having he tree out is great stage presence. plus you get an ax which makes a great b reverse kill move or Oos