You can create a group of issues on the chart that will be "wrapped" by parent task (summary element) and rendered underneath of it (Fig.1see example below). There are two possible ways to achieve such effect. First one, is creating a Story issue type and then adding sub-tasks to it, second method is using Epic. Each issue added to the Epic will be treated as a subtask and rendered in exactly the same manner as stories and sub-tasks.
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