IMO, the trees aren't the issue. Your problem is that there's a clear, unobstructed advance warning sign.
Absent this sign, then IMO an adjudicator would probably find that the signage did not meet the LATOR test of adequacy.
But with it? Although it doesn't convey all the same info that's on the gateway sign, it's not required to because it's not a regulatory sign in itself and what it does convey should have been sufficient to alert you.
Why didn't you see this sign or if you did, why did you think it didn't apply?