Why the vscode tree view file item has a larger indentation than it should be?

I am currently developing an Vscode Extension, it uses TreeView.
The TreeView works fine, but it has one problem:

Why the vscode tree view file item has a larger indentation than it should be?
(folder item seems have correct indentation)

Is there any config I missed? Or what are the potential causes?

As graph shows:

(for the code, its complex, not worth showing; I may update a easier one later.)

Update:

1. I made another simpler Normal Tree View, and the indentation is indeed there
   — its: file’s icon is aligned with the folder’s icon
   — its not: file’s icon is aligned with the folder’s > arrow
2. but, mine’s indentation is still even larger than that Normal one, Idk why
   — file’s icon is aligned with the folder’s icon + more to the right
3. I tried & found that the missing of align-icon-with-twisty css class is the key, but I have no idea why its missing (see graph)