We use a stack to build the tree from the expression: 3 4 + 5 *
Create a single-node tree and push it onto the stack.
1. Pop two trees (T2, then T1) from the stack.
2. Create a new root with the operator.
3. Attach T1 as the left child and T2 as the right child.
4. Push the new tree back onto the stack.
1. Read '3' (Operand)
2. Read '4' (Operand)
3. Read '+' (Operator)
4. Read '5' (Operand)
5. Read '*' (Operator)