Installation

In Blender open Edit, Preferences, Get Extensions, then use Install from Disk and pick the christmas_generator zip.

Usage

1. Open the Christmas tab in the 3D viewport sidebar (N) and pick what to make: Tree, Ornament, Lights or Wreath. Click Add, or use Shift+A, Mesh, Christmas Design. The design appears at the 3D cursor.
2. Click the picture or the arrows to pick another design. Surprise picks a random design, Vary changes the current one a little and Colors picks new colors.
3. Change the size, shape and materials with the sliders and picture choices below. On a tree, the Decorations box switches ornaments, lights, garland, topper, skirt, gifts, tinsel and candles on and off and picks the color scheme; the closed sections hold every detail.
4. Lights glow by themselves in Cycles and EEVEE. Set Animation to Twinkle, Fade or Chase to animate them.
5. Set the detail level from Low (game-ready) to Ultra (close-ups). Convert to Mesh keeps the design as plain meshes for export; Delete removes it with all its parts.