Combine 1½ cups flour, the yeast, and baking soda.
Heat buttermilk, shortening, sugar and 1 teaspoon salt till warm, stirring to melt the shortening. Add to the dry ingredients; add egg.
Beat at low speed for 30 seconds, scraping bowl constantly. Beat 3 minutes at high speed. Stir in enough remaining flour to make moderately stiff.
Turn onto a floured board; knead 5 minutes. Cover; let rest 10 minutes. Halve dough. Roll one half to a 14 x 6 inch rectangle. Spread with 1 tablespoon butter; sprinkle with red sugar crystals. Fold in half to make a narrow rectangle. Cut into fourteen 1-inch strips. Twist each one; arrange on a greased baking sheet in a tree shape. Repeat with the remaining dough, butter and green sugar crystals. Let rise 1 hour.
Bake in a 375-degree oven for 15 minutes; cool. Frost with powdered sugar icing, if desired.