in Dark Omen

Treeman is a huge monster-unit in DO. Its characteristics and traits are identical (or very close) to the characteristics mentioned in TT armybook. 
Despite the description in both DO and TT which states that Treeman can't wear armor it still has a special armor type which imbues its wearer with different traits like weakness to fire.
Treeman has 2 Armor rating which corresponds to 5+ save in TT. Whether it is unmodified save or not is unknown.