Common Ancestor | Python Fiddle

class Node:
    value = None
    left = None
    right = None
    def __init__(value, left=None, right=None):
        self.value = value
        self.left = None
        self.right = None

def isInTree(root, node):
    if root.value == node.value:
        return True
    elif root.left == None and root.right == None:
        return False
    else
    	return isInTree(root.left, node) or isInTree(root.right, node)
        
def isInLeft(root, node):
    if root.left.value == node.value:
        return True
    elif root.left == None:
        return False
    else:
        return isInTree(root.left, node)
    
        
def find(root, node):
    if root.value == node.value:
        return [root.value]
    if isInLeft(root, node):
        result = []
        result.append(find(root.left, node))
        result.append(root.value)
        return result
    else:
        result = []
        result.append(root.value)
        result.append(find(root.right, node))
        return result
def findCommonAncestor(root, nodeA, nodeB):
    isAInLeft = isInLeft(root, nodeA)
    isBInLeft = isInLeft(root, nodeB))
    
    if root.value == nodeA.value:
        result = []
        if isBInLeft:
            result.append(find(root.left,  nodeB))
            result.append(root.value)
        else:
            result.append(root.value)
            result.append((find(root.right, nodeB)))
        return result
    elif root.value == nodeB.value:
        result = []
        if isAInLeft:
            result.append(find(root.left,  nodeA))
            result.append(root.value)
        else:
            result.append(root.value)
            result.append((find(root.right, nodeA)))
        return result
    # If both in only one side of tree, recurse with root=root.left
    elif isAInLeft and isBInLeft:
        return findCommonAncestor(root.left, nodeA, nodeB)
    
    elif not isAInLeft and not isBInLeft:
        return findCommonAncestor(root.right, nodeA, nodeB)
    
    
    elif isAInLeft:
        result = []
        result.append(find(root.left, nodeA))
        result.append(root.value)
        result.append(find(root.right, nodeB))
        return result
    
    else:
        result = []
        result.append(find(root.left, nodeB))
        result.append(root.value)
        result.append(find(root.right, nodeA))
        return result
testTree=Node(2, left=Node(1), right=Node(3))
findCommonAncestor(testTree, Node(1), Node(3))

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