C++ :: Adding Mathematical Expression In Binary Tree

I want to add mathematical expression in a binary tree but I have some problems with the algorithm. I found this one:

-If the current token is a '(', add a new node as the left child of the current node, and descend to the left child.
-If the current token is in the list ['+','-','/','*'], set the root value of the current node to the operator represented by the current token. Add a new node as the right child of the current node and descend to the right child.
-If the current token is a number, set the root value of the current node to the number and return to the parent.
-If the current token is a ')', go to the parent of the current node.

Here is the code that I made so far:

template<class T>
void Tree<T>::Expr(Node<T> *node, char expr[], int &i) {
i++;
T x = expr[i];
if(x == '(') {
node = node->Left;

[Code] ....

I know that it is a big mess and it doesn't follow the algorithm but this is the problem. For example if the token is '(' I go to the left child of the current node. Then lets say that the next token in the expression is a number. I add this number to the current node and I must go back. But how can I go back to the parent? I will go back to line 13 and the program will end. What should be the structure that I must use?