Evaluate expression tree

ExpressionTree.java

public class ExpressionTree {
  public static int eval(MyTreeNode root) {
    return 0;
  }
}

ExpressionTreeTest.java

import static org.junit.Assert.*;

public class ExpressionTreeTest {
  @org.junit.Test
  public void eval() throws Exception {
    MyTreeNode five = new MyTreeNode("5", null, null);
    MyTreeNode four = new MyTreeNode("4", null, null);
    MyTreeNode two = new MyTreeNode("2", null, null);
    MyTreeNode three = new MyTreeNode("3", null, null);
    MyTreeNode times1 = new MyTreeNode("*", five, four);
    MyTreeNode times2 = new MyTreeNode("*", two, three);
    MyTreeNode plus = new MyTreeNode("+", times1, times2);

    assertEquals(26, ExpressionTree.eval(plus));
  }

}

MyTreeNode.java

public class MyTreeNode {
  private String data;
  private MyTreeNode left;
  private MyTreeNode right;

  public MyTreeNode(String data, MyTreeNode left, MyTreeNode right) {

    this.data = data;
    this.left = left;
    this.right = right;
  }

  public String getData() {
    return data;
  }

  public void setData(String data) {
    this.data = data;
  }

  public MyTreeNode getLeft() {
    return left;
  }

  public void setLeft(MyTreeNode left) {
    this.left = left;
  }

  public MyTreeNode getRight() {
    return right;
  }

  public void setRight(MyTreeNode right) {
    this.right = right;
  }
}