<human>:  I have a question about the paper Creating Expression Trees. Where does the expression tree come from?
<bot>: The expression tree is a representation of the expression. It’s a way of expressing the expression in a way that is easy to understand. For example, the expression “(2 + 3) * 4” can be represented as a tree. The tree has four nodes, and each node represents a different part of the expression. The first node is the left parenthesis, the second node is the addition, the third node is the multiplication, and the fourth node is the right parenthesis.