DataGrid Hierarchy checkbox-indeterminate

Good day,
I have a question about DataGrid Hierarchy. As shown below I want to see DataGrid Hierarchy with checkbox.
Unfortunately, I cannot activate the checkbox-indeterminate? How can I change settings so that it is activated?

just like here:
2023-02-13 11_30_05-Blazor checkbox component with optional tri-state support

You need to bind to bool? and set TriState to true:

Thank you for your answer, I set TriState to true. How can I define the bool value in my case?

You can set TValue="bool?".

I used it doesn't work.
here is the whole code:

Well, you might want to have tri-state CheckBox in the header instead for items.

Yes, that will work for me too. But I get the args error in the header area.