Line a baking sheet or work surface with parchment paper or a silicone baking mat. Arrange 12 pretzel rods several inches apart, leaving enough room for the green coating to spread around each tree.

Place the green candy melts in a completely dry microwave-safe bowl. Microwave in 20–30-second intervals, stirring thoroughly after each interval, until the coating is smooth; stir in the shortening or coconut oil only if the coating is too thick.

Transfer the melted coating to a piping bag or zip-top bag with a small corner snipped off, or keep it in the bowl and use a spoon. Pipe over the upper portion of each pretzel rod, beginning with a narrow zigzag near the top and making each lower zigzag progressively wider.

Leave the lower section of every pretzel rod uncovered so it looks like the tree trunk and gives you a convenient handle. Work with one tree at a time so the coating remains soft while you decorate.

Immediately scatter Christmas sprinkles and miniature candy-coated chocolates over each freshly piped tree. Press a few larger candies gently into the coating if needed, but avoid waiting because the surface firms quickly.

Let the pretzel trees stand at room temperature for 15–20 minutes, or refrigerate them for about 10 minutes, until the candy coating is firm. If desired, drizzle a small amount of melted white candy coating over the finished trees to resemble snow.