Gtk.TreeView.prototype.insert_column

function insert_column(column:Gtk.TreeViewColumn, position:Number):Number {
    // Gjs wrapper for gtk_tree_view_insert_column()
}

This inserts the column into the tree_view at position. If position is -1, then the column is inserted at the end. If tree_view has "fixed_height" mode enabled, then column must have its "sizing" property set to be GTK_TREE_VIEW_COLUMN_FIXED.