Sets the column to draw the expander arrow at. It must be in tree_view.
If column is NULL, then the expander arrow is always at the first
visible column.
If you do not want expander arrow to appear in your tree, set the
expander column to a hidden column.
Sets the column to draw the expander arrow at. It must be in tree_view. If column is NULL, then the expander arrow is always at the first visible column. If you do not want expander arrow to appear in your tree, set the expander column to a hidden column.