LayeredDigraphLayout not showing disconnected nodes

I have a graph with disconnected nodes

If I use a LayeredDigraphLayout, the disconnected nodes would not show up,

              isOngoing: false,
              layerSpacing: 20,
              setsPortSpots: false,
              columnSpacing: 20,
              isRouting: true,
              isValidLayout: true,
              isViewportSized: true,
              aggressiveOption: go.LayeredDigraphLayout.AggressiveMore,
              cycleRemoveOption: go.LayeredDigraphLayout.CycleDepthFirst,
              initializeOption: go.LayeredDigraphLayout.InitDepthFirstOut,
              layeringOption: go.LayeredDigraphLayout.LayerOptimalLinkLength,
              packOption: go.LayeredDigraphLayout.PackAll,

but the following tree layout would render the disconnected nodes, can you tell me how would I fix my LayeredDigraphLayout to display the disconnected nodes?

              comparer: go.LayoutVertex.smartComparer,
              alignment: go.TreeLayout.AlignmentStart,
              treeStyle: go.TreeLayout.StyleRootOnly,
              layerStyle: go.TreeLayout.LayerUniform,
              nodeIndent: 100,
              layerSpacing: 100,
              compaction: go.TreeLayout.CompactionNone,

I am unable to reproduce a problem with LayeredDigraphLayout not laying out disconnected nodes. If your layout direction is zero, those nodes are typically placed in the right-most column.

I am unsure what behavior you want. Perhaps the code in this topic will help: LayeredDigraphLayout Arrangements of Disconnected Nodes