tree array_to_tree (int *num, int inf, int sup) {
    tree result;
    if (inf > sup)
        result = NULL;
    else {
        unsigned int middle = (inf + sup) / 2;
        result = NULL;
        insert_tree (num[middle], result);
        result->left = array_to_tree(num, inf, middle-1);
        result->right = array_to_tree(num, middle+1, sup);
    }
    return result;
}