public void CallTree_CollapseAll()
        {
            CallTree tree = CreateCallTree();

            tree.CollapseAll();

            tree.TopLevelNodes[0].IsExpanded.Should().BeFalse();
            tree.TopLevelNodes[0].Children[0].IsExpanded.Should().BeFalse();
            tree.TopLevelNodes[0].Children[1].IsExpanded.Should().BeFalse();
            tree.TopLevelNodes[0].Children[2].IsExpanded.Should().BeFalse();
            tree.TopLevelNodes[1].IsExpanded.Should().BeFalse();
            tree.TopLevelNodes[2].IsExpanded.Should().BeFalse();
        }