I don't know of a way to remove the "+" when you set a toggle item, but you can use an expression in the hidden property of the items being toggled to have them expanded or collapsed and you can use the same expression in the InititialToggleState of the Toggle Item to have the "+" be a "-". In your example I'd use the expression:

=NOT(Fields.Parent.Value="IT")

So that would expand the items under the IT group and put a "-" next to IT and collapse the items in NON-IT and Other and put a "+" next to Non-IT and Other.