Christmas tree is a compound sign: first, sign Christmas, then sign tree. To sign Christmas, form the ASL letter C sign with your dominant hand, swoop it down in front of you, then scoop it back up until your dominant forearm is upright and your 'C' hand holds steady.
To make the tree sign, take your non-dominant hand and extend it flat across your body to make the ground. Then take your dominant hand and stand it up at right angles, with your fingers extended and pivoting back and forth at the wrist, like the swaying leaves and branches of a tree.
Teach your baby or toddler the Christmas tree sign in the context of setting up the holiday decor, or when you head out to the village and see all the varieties of Christmas trees lining the streets and store windows.
This is a useful flash card taught best to toddlers in conjunction with other Christmas holiday flash cards.