True to mark this column as a checkbox column. Checkbox columns show
checkboxes instead of text. Whenever an item's text in a checkbox column is set to
"On", "True", or "1", the checkbox will be selected. All other item texts will lead
to an unselected checkbox.
You can modify the states of the checkboxes by using the Treeviewleaf.SetState method. Similarly, getting the state of a checkbox is possible via the Treeviewleaf.GetState method.
To get notified whenever the user toggles a checkbox state, you have to listen to the Treeview.ValueChange attribute.
Also note that Treeviewcolumn.Checkbox and Treeviewcolumn.Editable and Treeviewcolumn.Icon are mutually exclusive. You cannot create checkbox columns that are editable or show icons.
Checkboxes in the first treeview column are currently unsupported on Windows, macOS, and Linux.