The achievement is located in the 9th chapter called "Wintersun".
At the moment is unclear what counts exactly, so I show you all the snowy stuff in this chapter. Perhaps the community can help to clear this achievement to 100%
We have 3 option in my opinion what counts for the achievement:
1) all the snowy stuff in this chapter (the videos shows this)
2) only the branches with attachment points for Yarni, without all the other trees / branches with snow
3) other unclear things because for the most people (me too) unlocks the achievement before point 1 or 2 is "done"
At the moment, I recommended you clear all the snowy stuff in this chapter to get the achievement.