| Branch(l, col, r) ->
let (lead',left_score) = tree_best_sofar l lead in
let (lead'',right_score) = tree_best_sofar r lead' in
| Branch(l, col, r) ->
let (lead',left_score) = tree_best_sofar l lead in
let (lead'',right_score) = tree_best_sofar r lead' in