The return value for ttk.style().map('Treeview') is wrong for the 'background' value in the 'alt' theme: tuple are missing.

Tcl alt Treeview map:

-foreground {disabled #a3a3a3 {!disabled !selected} black selected #ffffff} 
-background {disabled #d9d9d9 {!disabled !selected} #ffffff selected #4a6984}


tkinter alt Treeview map:

{
'foreground': [('disabled', '#a3a3a3'), ('!disabled', '!selected', 'black'), ('selected', '#ffffff')], 
'background': ['disabled', '#d9d9d9', '!disabled !selected', '#ffffff', 'selected', '#4a6984']
}

It should be:

'background': [('disabled', '#d9d9d9'), ('!disabled !selected', '#ffffff'), ('selected', '#4a6984')]