Having only children-less elements loading asynchronously

[The-BlackWidow]

Hi,
Working with vuejs, let's say I have a tree with :

• Folder-0
  • Folder-0.1
  • Folder-0.2
  • Item-0.1
  • ...
  • Item-0.200
• ...

Because my items are so numerous, I'd like to load them asynchronously, while all the subfolders (= tree elements with children) are preloaded.

I tried both parts: loading asynchronously my items and loading only the folders and subfolders, but I can't figure out the proper syntax for mixing both.
Do you have a clue ?

Thank you.