gtk-tree-store-set (store iter &rest values)

store -- a gtk-tree-store object
iter -- a valid gtk-tree-iter iterator for the row being modified
values -- the values to set

The gtk-tree-iter iterator for the row being modified.

Sets the values of one or more cells in the row referenced by iter. The variable argument list should contain the values to be set.

(let ((model (gtk-tree-store-new "gchararray" "gchararray" "guint")))
  ;; First Book
  (let ((iter (gtk-tree-store-append model nil))) ; Toplevel iterator
    ;; Set the toplevel row
    (gtk-tree-store-set model
                        iter
                        "The Art of Computer Programming"
                        "Donald E. Knuth"
                        2011)
    ;; Append and set three child rows
    (gtk-tree-store-set model
                        (gtk-tree-store-append model iter) ; Child iterator
                        "Volume 1: Fundamental Algorithms"
                        ""
                        1997)
  ... ))    

The Lisp implemenation does not support pairs of a column index and a value, but a list of values. Therefore, it is not possible to set individual columns. See the function gtk-tree-store-set-value for setting the value of single columns.