class Tree {
}

var tree = Tree();

tree.b = "A";
tree.b += "B";
print(tree.b); # expect: AB


tree.x = 5;
print(tree.x); # expect: 5
tree.x = 6;
print(tree.x); # expect: 6
tree.x *= 2;
print(tree.x); # expect: 12
tree.x *= "Test"; # expect runtime error: Operands must be numbers. Got: [12, Test]
print(tree.x);