Not sure I understand what you are trying to do as one of the main features of Project is to take small tasks and show how these fit together and hence show how long the overall task takes!
That aside, it is possible to colour code bars on youe GANTT chart and you could use this to distinguish between the different levels.
Go to Format\Bar Styles. Use Flags to identify the various levels. You can add columns to the table by right clicking on the titles bar of the tagle and selecting Insert Column. Use this to show Flags 1-3 which you set to show if a task is level 1, 2 or 3.