Very simple and quick method for manufacturing of frames into which you can insert what you want.
Take a thick paper (Whatman possible) I have for drawing, in any format. On each side of the point to note 4 to 1.5 cm. and hold the line. Should get here this grid
Cut the corners.
2 line note 1.5 cm
And draw a trapezoid, that’s right
Cut a trapezoid
It should look like this. Trapezoid can be drawn as to the long and short side.
Burst line than you prefer and bend.
Insert one area to another
Frame is obtained. If the back side of the paper to glue something like adhesive film under the tree you get a frame under a tree.