If your state machine has high number of states (e.g. more than 10) its diagram may de difficult to analyze and manage. To simplify the structure of the diagram you can replace a group of state bubbles on the diagram with one hierarchical state. Place a new state bubble, right-click it and select Hierarchical State from the context menu to turn the new state to a hierarchical state (cyan color). You can then push into the hierarchical state, move the desired states inside the new state and re-establish connections with the rest of the diagram. See on-line documentation on State Machine editing for more info.