There are several shots in the movie showing a 360 degrees panorama of the environment around a fixed location.
It feels like the point of view of some of the characters, that would scan their surroundings for potential dangers.
We viewers are very attentive during those shots; it is like if we shared the same burden as the characters, we are looking out for danger.
During the shots of the tree canopies, I would say that we can feel like the character, exhausted of continuously having to worry and check the surroundings, wishing we could just take a short break (by looking at the sky), but still very conscious that it might be fatal.
I think it contributes to the atmosphere of the movie, that is both oppressive and grim.