get_model
Description:
Returns the model the `GtkTreeView` is based on.
Note: 
      
        
    
    Use [class@Gtk.ListView] or [class@Gtk.ColumnView] instead
Returns null if the model is unset.
Parameters:
| this | 
           a `GtkTreeView`  | 
      
Returns:
| 
           A `GtkTreeModel`  |