this video describes the formation of ice crystals through Bergeron-Findeisen process and also explain the Collision-Coalescence process.
the important links are:
https://kidsgeo.com/geography-for-kids/collision-coalescence-of-precipitation/
and:
https://danatobin.weebly.com/uploads/2/8/4/4/28441795/bergeron_process.pdf
