you create full tree at start and that's so slowly when you have a big folder tree. maybe you create dynamic load data when user expand folder?

for example - create closed folders and just 2 levels deep for all. when user expand folder - read one more level deep only for this item.

second option it's a caching. you don't need to read data again if it's loaded...

i modify code to use in Python and its worked. I like to use it but its so slowly ((