In a large bowl, slowly add the water to the baking soda so that you form a paste that is consistent with a grainy toothpaste. I did not use my entire 1 cup of water.
Add the sprinkles and sequins to the paste.
Have your child use their hands to form the paste into a Christmas tree form on a baking sheet.
Use an eyedropper, small cup or spray bottle to add vinegar to the Christmas tree baking soda mixture.
Video
Notes
If you find your mixture is too runny and not holding up its shape, then add more baking sode.If you find that your mixture cannot be formed into a shape because it is too dry, add more water a little bit at a time.