how to disselect the selected option in single valued tree ( isMultiple = false ) ?

[Raviteja-k-naik]

I have a combo tree with multiselect false.
If i select an option in single select tree and want to clear selection right there (i.e., not through any external button click to clear).

In my case, there are categories say,
cat 1 (id=1)
cat 1.1 (id=2)
cat 1.1.1 (id=3)
cat 1.2 (id=4)

--> if i select 'cat 1' with id=1, then clear the option( i.e., by using Backspace in keyboard) and send the form
--> when I click send form then it sends value with id=1 ( 'cat 1' option) instead of null

So, is there any function or feature that can clear selected value in single select tree.

Thanks.