Hint Resolve tree_rep_nullval: saturate_local.

Lemma treebox_rep_leaf: forall x p b (v: val),
is_pointer_or_null v ->
Int.min_signed <= Z.of_nat x <= Int.max_signed ->
data_at Tsh t_struct_tree (Vint (Int.repr (Z.of_nat x)), (v, (nullval, nullval))) p * data_at Tsh (tptr t_struct_tree) p b |-- treebox_rep (T E x v E) b.