I don’t think it’s a strange question. Since pastels layer so well, I’d just do the background and mid ground and then put the tree on top. Lighter colors layer on top of dark colors easily with pastel, I think the most challenging part may be the dark leaves against the darkest blues in the sky. Maybe lighten the value of the leave a little to make the leaves stand out. Then after the tree is in place go back and reinforce some sky holes with the blues or colors of your choice. Those are my thoughts, but I’m sure that are other ways to do it too.