Behavior allows you to change how certain tasks are represented in the chart.

Treat parent issues as groups

A group aggregates values from the tasks it contains, and its own values for manual start date, finish date or work estimation are ignored. You can configure your Gantt chart to show parent issues either as actual tasks or as groups (containers for tasks). 

Grouped tasks

Structure.Gantt groups issues by default. To have your parent issues shown as actual tasks, on the Scheduling screen, under Groups, uncheck the "Treat parent issues as groups" checkbox.

Configuring scheduling behavior

If a parent issue contains non-issue items only (folders), it will be shown as a task, regardless of the selected option.