Nested Call Expression Evaluate operator Evaluate operands 3 Apply! 45 add(add(6,mu1(4,6),mu1(3,5)) add 30 15 add(6,mu1(4,6)) mu1(3,5) 24 add 6 mu1(4,6) mul 3 5 mul 4 6 Expression TreeNested Call Expression Evaluate operator Evaluate operands Apply! add(add(6, mul(4, 6)), mul(3, 5)) add 1 2 3 add(6, mul(4, 6)) add 6 mul(4, 6) mul 4 6 24 30 mul(3, 5) 15 mul 3 5 45 Expression Tree