1    def makeTree(self, postFix, stk):
2        for symbol in postFix:
3            if self.isOperand(symbol):
4                newPtr = self.treeNode(symbol)
5                stk.push(newPtr)
6            else:
7                ptr1 = stk.pop()
8                ptr2 = stk.pop()
9                newPtr = self.treeNode(symbol)
10               newPtr.left = ptr2
11               newPtr.right = ptr1
12               stk.push(newPtr)
13       return stk