This is the interior of the pine tree Mickey chooses, then chops down, little knowing Chip and Dale are inside!
This is a beautifully composed B/G. Note the the dark splay of needles on the edges, and the bright "lighting" at the center, all contributing to a beautiful stage for the animation to play out.
Then there's the "background within a background," with its delicate palette of yellows and greens.
Lovely!
And there's more to come...