Gtk.TreeView.prototype.set_expander_column

function set_expander_column(column:Gtk.TreeViewColumn):void {
    // Gjs wrapper for gtk_tree_view_set_expander_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.