// Nœud opérateur
    public class OperatorNode extends Node {
        String operator;
        Node left, right;

        OperatorNode(String operator, Node left, Node right) {
            this.operator = operator;
            this.left = left;
            this.right = right;
        }

        @Override
        public String toInfix() {
            // On ajoute systématiquement des parenthèses autour de chaque opération
            if (operator == "*"){
                return "(" + left.toInfix() + " x " + right.toInfix() + ")";
            }
            return "(" + left.toInfix() + " " + operator + " " + right.toInfix() + ")";
        }
    }