import collections
class TreeNode:
    def __init__(self, data, left = None, right = None):
        self.data = data
        self.left = left
        self.right = right
def insert(temp,data):
    que = []
    que.append(temp)
    while (len(que)):
        temp = que[0]
        que.pop(0)
        if (not temp.left):
            if data is not None:
                temp.left = TreeNode(data)
            else:
                temp.left = TreeNode(0)
            break
        else:
            que.append(temp.left)
        if (not temp.right):
            if data is not None:
                temp.right = TreeNode(data)
            else:
                temp.right = TreeNode(0)
            break
        else:
            que.append(temp.right)
def make_tree(elements):
    Tree = TreeNode(elements[0])
    for element in elements[1:]:
        insert(Tree, element)
    return Tree
def search_node(root, element):
    if (root == None):
        return None
    if (root.data == element):
        return root
    res1 = search_node(root.left, element)
    if res1:
        return res1
    res2 = search_node(root.right, element)
    return res2
def print_tree(root):
    if root is not None:
        print_tree(root.left)
        print(root.data, end = ', ')
        print_tree(root.right)
def solve(root):
    q = collections.deque([root])
    p, visited = dict(), set()
    while q:
        cur = q.popleft()
        if cur in visited:
            grand_p, is_left = p[p[cur][0]]
            if is_left: grand_p.left = None
            else: grand_p.right = None
            return root
        visited.add(cur)
        if cur.left:
            p[cur.left] = (cur, 1)
            q.append(cur.left)
        if cur.right:
            p[cur.right] = (cur, 0)
            q.append(cur.right)
    return root
root = make_tree([5, 3, 7, 2, 4, 6, 8])
link_from = search_node(root, 4)
link_to = search_node(root, 6)
link_from.right = link_to
print_tree(solve(root))

root = make_tree([5, 3, 7, 2, 4, 6, 8])
link_from = search_node(root, 4)
link_to = search_node(root, 6)
link_from.right = link_to

2, 3, 5, 6, 7, 8,