How to make a link always straight

I have a TreeLayout like this:

myDiagram = $(go.Diagram, "goeditor", {
    "undoManager.isEnabled": true,
    scrollMode: go.Diagram.InfiniteScroll,
    allowMove: false,
    layout: $(go.TreeLayout, {
      nodeSpacing: 138,
      layerSpacing: 117,

and my linkTemplate:

      routing: go.Link.Orthogonal,
      corner: 500,
      smoothness: 1,
      curve: "Bezier",
      selectable: false,

link I want:

But sometimes it’s not straight:

Any idea how to make the link always straght? By the way, I don’t need to move the nodes.

If there were just two child nodes, would you want to guarantee that one link was straight? What would you want when there are four children? Or when one node is much taller than its siblings?