A copper nail, specifically (drill a hole first).

Some jurisdiction will make you replace the tree in that case, just to avoid this sort of mechanism.

Yeah but the tree only has to be that diameter at final size. You can plant a dozen tiny trees too close then let them stunt or choke each other out

Some jurisdictions seem to be attempting to counter this sort of thing, and an aspect is: if you can't do it properly, we will, and send you the bill at our chosen rates. And we are going to check.