C#

private void timer_Elapsed(object state)
{
    if (Dispatcher.CurrentDispatcher != _dispatcher) 
// _dispatcher is a reference to the Dispatcher under wich the Timer was instantated
    {
        _dispatcher.Invoke(
        new System.Threading.ThreadStart(delegate
        {
            onTick();
        }), DispatcherPriority.Send); 
    }
    else
    {
        onTick();
    }
}

private void onTick()
{
    if (Tick != null)
    {
        Tick(this, new EventArgs());
    }
}

private Point PositionNodes(List<Node> nodes, Point point)
      {
         // Create new start point for downwards line
         Point newStartPoint = new Point();
         Point newFinishPoint = new Point();
         newStartPoint = point;

         int nodeHeight = nodes[0].Size.Height;

         // Loop nodes
         for(int i = 0; i < nodes.Count; i++)
         {
            // Set node location and draw
            nodes[i].Location = point;

            // Increase Y by one line
            point.Y += nodeHeight;

            // If node has child nodes
            if (nodes[i].Nodes.Count > 0 && nodes[i].Expanded)
            {
               // Call method again on child nodes
               point.Y = PositionNodes(nodes[i].Nodes, new Point(point.X + m_xIndentation, point.Y)).Y;
            }

            // Set finishing point of line
            newFinishPoint = point;
            newFinishPoint.Y -= (int)(nodes[0].Size.Height * 0.5);

            // If node has only one child and is expanded reduce line by this amount
            if (nodes.Count == 1 && nodes[i].Expanded)
            {
               // Reduce line by child nodes amount
               newFinishPoint.Y -= AmountToDeduct(nodes[i].Nodes);
            }

            // Add points to list
            m_linePoints.Add(newStartPoint);
            m_linePoints.Add(newFinishPoint);
         }

         // Cumulative height of nodes
         return point;
      }