Here's a simple little Christmas tree pin that can be as different as you want it to be.
Knife or rotary tool
1/4 inch thick basswood
safety glove and thumb quard
scroll saw or coping saw
small artists brush
small beads or 3-D fabric paint
adhesive to attach pin back
Start by drawing or tracing the Christmas tree onto 1/4 inch thick Basswood, and cutting the blank out. Some times I leave a "handle" on the blank. Because of the small size of the pin it's nice to have something to hold onto when whittling or carving. After the tree is carved, the handle can be cut off.
The first cuts should be to taper the tree to its top, and to begin to "round" it over to its sides to give it some shape.
The next cuts should be stop cuts across the tree, and remove wood up to these stop cuts. Again, round the sides over a bit for shape.
Finally, make a stop cut separating the tree trunk from the tree itself, and remove the wood up to this stop cut.
Paint the tree, and the trunk. Green for the tree and brown for the trunk. Add a bit of white at the ends of the tree branch sections for the snow.
I like to also add some tree lights. In this example, I use 3 D fabric paint. Just squeeze a bit out of the bottle applicator for each "light". This fabric paint will dry rounded and make a good light.
Just add the pin back and you've got a real nice little pin. This example is small, but a larger one is done the same way, and might be a better choice for a young or less experienced whittler. A rotary tool and sanding sleeve works great too.