Showing and Hiding Hierarchy Levels 
When you display a list as a hierarchy, you can show or hide subordinate data.
A hierarchy level is created in the first column from every hierarchy column. Each entry of a hierarchy level that contains subordinate data is indicated by a small arrow icon. Lower hierarchy levels are slightly indented. Data from the lowest hierarchy level is indicated by a point.
Example
The Airline Carrier column contains the names of the airline carriers The Airline column contains the names of airlines. All other columns contain data that describes the flights of each airline in detail, for example, flight date, price, and so on.
You have set the Airline and Flight Number columns as hierarchy columns. In the first column, Airline/Flight Number, the flight number is listed (slightly indented) under every airline.
Each airline and flight number is indicated with an arrow icon. The rows in the lowest hierarchy level, which contain the data for the flight date, price, and so on, are indicated with a point.
You can show and hide the subordinate entries of a hierarchy by choosing the small arrow icon for that hierarchy level.
Prerequisites
You are displaying a list as a hierarchy
For more information: Showing and Hiding Hierarchies.
You have set at least one hierarchy column
For more information: Settings Hierarchy Columns.
Procedure
To show the subordinate data of an entry in the first column, select the entry.
The direction of the arrow icon switches from To the Right to Down.
To hide the subordinate data of an entry in the first column, select the entry.
The direction of the arrow icon switches from Down to To the Right.