According to the documentation (https://www.tcl.tk/man/tcl/TkCmd/ttk_treeview.htm) the item option "values" is "The list of values associated with the item.", and the item option "tags" is "A list of tags associated with this item." Tcl's list corresponds Python's tuple (lists are also accepted in Python 3).

Change your example to:

    kw = {'values': ('" ";',), 'tags': ()}