def getExpressionTree(postfix):
    stack = []
    for char in postfix:
        if (char == ' '):
            continue
        elif (not isOperator(char)):
            t = Node(char)
            stack.append(t)
        else:
            t = Node(char)
            t1 = stack.pop()
            t2 = stack.pop()
            t.right = t1
            t.left = t2
            stack.append(t)
    t = stack.pop()
    return t
def getExpressionTree(postfix):
    stack = []
    for char in postfix:
        if (char == ' '):
            continue
        elif (not isOperator(char)):
            t = Node(char)
            stack.append(t)
        else:
            t = Node(char)
            t1 = stack.pop()
            t2 = stack.pop()
            t.right = t1
            t.left = t2
            stack.append(t)
    t = stack.pop()
    return t