Sub-Process Events
If an event in the Event Viewer has a 
character to the left of the event, it means it is a sub-process start event.
For example:
Clicking on the character expands the list to include the events related to the sub-process that was started. The events related to the sub-process are shown indented below the sub-process start event:
Sub-processes can be many levels deep, that is, a task in one process can start another process, which can contain a task that starts another process, and so on. Each time another sub-process is started, the event hierarchy is shown with additional characters that can be expanded. For example:
By default, a maximum of 100 events will be shown under a sub-process start event (although this number is configurable by a system administrator). Which means that if there are more than 100 events related to the expanded sub-process, you will not be able to see them by expanding the list in this way. An alternative is to select the “Started instance” event, then select “This instance” from the Links menu to create a new event list containing all of the events related to the sub-process instance that was started.