Custom Delegate in multi hierarchy QTreeView

I have a multi hierarchy QTreeView (currently 3 levels, will be more depends),
I created 3 different delegates (delegate A/B/C) for each level
But how do I apply the delegate to the QTreeView properly?
The following pic shows what I want:

Code:

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>Row 0 -------------------- delegate A
>Row 1 -------------------- delegate A
 
^Row 2 -------------------- delegate A
  ^Row 20 ----------------- delegate B
     Row 200 -------------- delegate C
     Row 201 -------------- delegate C
     Row 202 -------------- delegate C
 
  ^Row 21 ----------------- delegate B
     Row 210 -------------- delegate C
     Row 211 -------------- delegate C
     Row 212 -------------- delegate C

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This function:
QAbstractItemView::setItemDelegateForRow(int row, QAbstractItemDelegate * delegate);

With this function, I can only assign the delegate for the first level of the TreeView.
And its children (level 2, level 3) are gonna share the same delegate with level 1

How do I assign the delegate B to Row 20 and Row 21?
How do I assign the delegate C to Row 200, Row 201, Row 202......