I agree with Barb. I would use silver or gold to quilt the tree, making the quilting look like garlands and ornaments. I might even use several colors for this. For the background I would quilt "presents" at the bottom in contrasting colors, then quilt the background of a room (walls, curtains, etc.) in the upper part of the background. I would make it subtle so you don't notice the background at first, but are drawn into it when you study the quilt.