Hide with asterisks a ttk.Treeview column

I'm trying to hide a password column values in a ttk.TreeView.

At the moment is like this:

res_table = ttk.Treeview(res_w, columns=heading,                       
show='headings', selectmode='browse')


for el in heading:
    res_table.heading(el, text=el)
    res_table.column(el, anchor='center', width=125, minwidth=125)

for row in result:
    for field in row:
        res_table.insert('', 'end', values=field)

Now, one of the el elements has value pw, I would like that column to be display its values as asterisks not plain text, how do I do that?