Here's the C API:

void                gtk_tree_store_append               (GtkTreeStore *tree_store,
                                                         GtkTreeIter *iter,
                                                         GtkTreeIter *parent);

It will append an iter to tree_store and set it in the iter variable. It does nothing else.

Now, GtkTreeStore.append() works another way (it's overridden):

model.append(parent, row)

where row is a tuple containing the values for each column.

A few things are wrong here:

 + it forces me to make sure that the row tuple will always have the values for the columns in the right order. Usually, I have no real interest in the order of my columns and I use variables like COLUMN_NAME = 0, COLUMN_ICON = 1, etc.

 + the C and the python API don't work the same way, and the user will assume they will since they have the same name. I think the python API provided here is useful, but it should come with another name.