BST insert using recursive

[hichipi12]

I am working on implementing an insert function in BST. When I print out the bst out, there are two true and two false. It supposed to be all true. I do not know what have i done wrong. I would appreciate if anyone can help me

class BTNode:
    def __init__(self, value, left, right):
        self.value = value
        self.left = left
        self.right = right
class BST:
    def __init__(self):
        # reference to root node - do not modify
        self.root = None
    def insert(self, value):
        '''Takes a numeric value as argument.
        Inserts value into tree, maintaining correct ordering.
        Returns nothing.
        recursive, may use helper function'''
        if self.root is None:
            self.root = BTNode(value, None, None)
        else:
            self.insert_helper(value, self.root)
# self.root = node in the parameter
    def insert_helper(self, value, current_node):
        if value < current_node.value:
            if current_node.left is None:
                current_node.left = BTNode(value, None, None)
            else:
                self.insert_helper(value, current_node.left)
        elif value > current_node.value is None:
            if current_node.right:
                current_node.right = BTNode(value, None, None)
            else:
                self.insert_helper(value, current_node.right)
    def search(self, value):
        if self.root:
            value_found = self.search_helper(value, self.root)
            if value_found:
                return True
            return False
        else:
            return None
    def search_helper(self, value, cur_node):
        if value > cur_node.value and cur_node.right:
            return self.search_helper(value, cur_node.right)
        elif value < cur_node.value and cur_node.left:
            return self.search_helper(value, cur_node.left)
        if value == cur_node.value:
            return True

bst = BST()
for value in [4, 2, 5, 3, 1, 6, 7]:
    bst.insert(value)
print(bst.search(1))
print(bst.search(2))
print(bst.search(6))
print(bst.search(7))

Output:
True
True
False
False