In small bowl, stir together dip ingredients. Cover; refrigerate at least 1 hour to blend flavors.
Rinse and thoroughly dry vegetables. Trim broccoli and cauliflower floret stems.
Arrange broccoli on serving platter to form tree shape and tomatoes to form garland. Arrange bell pepper to form star and cauliflower to form snow (see photo). If desired, cover and refrigerate up to 4 hours.
Just before serving, arrange pretzels at bottom of tree to form trunk. Serve with dip.