frost on trees; hoarfrost on trees
General term for ice crystals formed on trees by freezing fog or moisture. Often used in meteorological contexts.
It was so cold this morning that frost had formed on the trees in the mountains.
snow monsters; frost-covered trees
Refers specifically to the dramatic, large-scale frost formations on trees in certain regions like Zao, where they are called 'snow monsters'. More of a tourism and local term.
The frost-covered trees of Zao are famous as 'snow monsters'.