Parent and Child Nodes
Each Rule or Action is comprises of Parent and Child nodes.

The root node ("Rule For") is displayed at the top, and can be considered the top-level parent node. Conditions are child nodes of this root.
Child nodes are a requirement for many Predicates. Any expected Child nodes are automatically added to the Parent, and are marked in grey with the component type.

Expanding and Collapsing Nodes
Nodes can be expanded and collapsed using the arrow in the top left of a node. When Collapsed, all Child nodes are hidden from view but the summary is displayed to the right of the Parent node.

You can also use the right-click context menu to Collapse Children or Expand Children.