The default Business Process Renderer is the Tile Renderer. It always shows one level of your tree, enriched with badges giving some hint on lower level node problems. This is what it looks like:
Please click on Tree below the breadcrumb to switch to the Tree View. In the left corner of every Tile you can find two icons, both of them will show the related sub-process. On your mobile phone this usually replaces your current view, please use the breadcrumb to navigate back to a higher level.
On a Notebook or Desktop Computer this usually leady to a split-screen view:
This example shows a subtree shown with the Tree Renderer, it is of course also perfectly legal to drill down using the Tile Renderer only.