title: tkinter treeview change column font size
body: <p>Right now i have this threecode:</p>
  
  <pre><code>tree["columns"] = ("one", "two", "three")
  tree.column("one", width=150)
  tree.column("two", width=150)
  tree.column("three", width=150)
  tree.heading("one", text="Naar")
  tree.heading("two", text="Spoor")
  tree.heading("three", text="Vetrektijd")
  tree['show'] = 'headings'
  </code></pre>
  
  <p>but what i want to do is change the font size to 20 of the three columns
  But how can i do that?
  Since on the internet i read something about Style() but that doesnt work in my code</p>