code: func (v *TreeStore) Append(parent *TreeIter) *TreeIter {
  	var ti C.GtkTreeIter
  	var cParent *C.GtkTreeIter
  	if parent != nil {
  		cParent = parent.native()
  	}
  	C.gtk_tree_store_append(v.native(), &ti, cParent)
  	iter := &TreeIter{ti}
  	return iter
  }
docs: // Append is a wrapper around gtk_tree_store_append().