IntelliGantt for Google support a traditional task hierarchy whereby summary tasks can contain any number of sub tasks. The hierarchy can be as deep as you like. Each level of the hierarchy has a small indent that affects the positioning of the associated task image and display name. Summary tasks containing sub tasks are represented as a folder. The Project Summary Task is represented as a folder with a star.
Starting with an empty project, select the project to establish your starting point and click on the '+' button to bring up the options for adding tasks. If you think of the current selection as a starting point, the options make more sense as to where the new tasks will end up. If you didn't want a new task in a particular position you can always click 'Undo'.
Here we have created six sub tasks by repeatedly clicking the 'Child Below' plus button. The project task has become a folder with a star to show it is the Project Summary Task. We will use in-place editing to rename the tasks.
You can indent tasks by dragging and dropping the image in the task's display name field. Use the left-mouse button or your finger and hold on the task image you wish to indent, then move to the right. As you move you'll see the 'new' summary task turn into a folder. Release to commit the change.
You can also select a new starting point and, just as we did with the Project Summary Task, use the 'add' tool to add new tasks as children to our selection.
You can indent a task several levels at a time depending how far you drag it. Here we do the same operation with task 'Five' so that it becomes a child of our 'New Task'.
As you would expect, you can outdent a task by using the same drag and drop movement, only to the left. As you move, IntelliGantt for Google will provide feedback as summary tasks become normal tasks again.