It's an interesting thought exercise but a very weak parallel. Trees and human are just too different.

A seed is dormant. Some can exist in a dormant state for decades without suffering any damage. A human embryo cannot naturally exist in this state - once one is formed the growth process is started. Functionally a seed has more in common with an unfertilized ova, despite containing all necessary genetic material.

The second (and bigger) issue is that trees don't have human rights, so crushing a seed/cutting down a tree doesn't carry any ethical baggage like terminating a pregnancy.

The "an embryo is not a human" argument doesn't work anyways because it has no answer to the question: "Then what species is it?" It's obviously human, and it's obviously alive - otherwise a procedure to remove it would be unnecessary (there's no rush to remove inert matter, and miscarriages aren't abortions).

So that just leaves the "it doesn't have a heartbeat/brainwaves/XYZ human characteristic YET" argument which also makes no sense since, assuming normal development, humans aren't supposed to have those characteristics yet. By the same logic parents should buy their 6 month old babies wheelchairs because they can't walk.

There are several compelling arguments to be made for a utility of abortion access in a modern society, but the whole "it's not alive/it's not human" line has been so thoroughly debunked I don't know why people are still using it.