def check_binary_search_tree_(root):
    # create helper function
    def check(root, min_value, max_value):
        # base case
        if root is None:
            return True
        
        # general case
        if root.data < min_value or root.data > max_value:
            return False
        
        return check(root.left, min_value, root.data - 1) and check(root.right, root.data + 1, max_value)
    
    return check(root, 0, 10000)

def inorder_list(root):
    values = []
    def inorder_t(root):
        if root is None:
            return
        inorder_t(root.left)
        values.append(root.data)
        inorder_t(root.right)
    inorder_t(root)
    return values

def check_binary_search_tree_(root):
    if root is None:
        return
    values = inorder_list(root)
    if values == sorted(values) and len(values) == len(set(values)):
        return True
    else:
        return False