Well, change the description for one thing. I believe we were also planning on dropping the needles and shed snow attacks.
All good potential abilities, but perhaps we should hammer down its theme? Is it an undead standard treant that succumbed to cold? Or is it an undead frost treant of some other genesis?
That works for me. In that case, just take frost treant's ability scores (with no Con score, of course), and perhaps boost Cha a bit (as is common for undead templates)?
These don't feel like "unholy toughness" type of undead, so I'd probably go with a boosted DR. Maybe slashing and cold iron? Or add some kind of vampire-style fast healing?

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.