First, arrange all the cut parts.
a. Assemble the Christmas tree, and plug the Christmas tree b with the star upwards into the Christmas tree a;
b. Select the yellow ribbon b*2 as shown in the right picture, and place it on the diagonal of the Christmas tree;
c. Then put another set of yellow ribbon a*2 on the other diagonal of the Christmas tree, and plug it into the yellow ribbon b;
d. Select the red gift box b*2 and place it on the diagonal of the bottom of the Christmas tree;
e. Select the longer part of the bottom of the red gift box a and plug it into b, and also place it on the diagonal.