Against 4-3-2-1 Christmas tree

[Accyrover]

The Christmas tree is a very good attacking formation, picture the formation in it's full attack phase, his DL/DR MR/ML will be motivated.
So it becomes, 2-3-4-1 and that is if his DL&DR are not blocked, in defence the whole pyramid floats backwards into a very strong defensive unit attacking it through the centre will be difficult.
IMO the way to crack this system open is to let him attack you he has no DM players so once committed to attack there is a huge gap between his MF and defence which if you are quick enough will consist of two players at best, this is where to exploit it's weakness
I would use.
3-6-1

------DC--DC--DC
-----DML---- -DMR
MR----------------------ML
------AMR------AML
------------ST

Block his MR/ML feeding his AMC and you stop his game. His lone MC is picked of by either the spare DMC or the DC.
Your AM stop his DR/DL attacking you.
AS I said I'd go defensive and hit him on the counter with long balls through the centre, but six MF players also gives you good possession if you want to play through him with short passing.