Write a program to prompt the user to enter a postfix expression. When the user presses enter, the stack based method for constructing expression trees will be executed. Use your stack from the previous question. You should implement your own ExpressionTree class to store the expression. Once the tree has been built, you should display it properly to the to the screen. Make sure that your printing routine properly displays the nodes in order (that is, a scan from left to right, ignoring the vertical location of nodes, should read the nodes of the tree in-order).
