In advance, make snowflake candy plaque by pouring melted white candy 1/2 in. deep in snowflake pan. Mold large petals of snowflake only. Refrigerate until firm; unmold into soft towel. Mold snowflakes for tree using nesting cutters- 3 of each size except mold 2 of smallest size. Place cutters on parchment paper-covered board; pour candy 1/4 in. deep. Refrigerate until firm; unmold. Add vein designs to large plaque and tree snowflakes with melted candy in cut parchment bag. Mold 6 chocolate and 12 white vein pieces by piping melted candy in vein areas on outside of pan. Refrigerate until firm; unmold.
Ice 2-layer cake (3 in. high) lightly with buttercream. Prepare 2 1/2 recipes of ganache glaze and cover cake; let set. Place cake on foil-covered board; dowel rod cake where plaque will be postitioned. Pipe freehand snowflakes on sides with melted candy in cut bag, piping 3 intersecting lines with "v" shapes at tips.
Position candy plaque and chocolate vein insets. Position 6 white veins on cake between petals; attach 6 to plaque at petal intersections with melted candy. To assemble candy snowflake tree, stack largest to smallest snowflakes with 2 hollow-center candies between each layer, attaching with melted candy. Add 1 small snowflake on top layer; position the other upright.