Project and regular tasks

I want to know if the effect in the picture can be achieved?The project timeline is calculated based on the task timeline. How to set it?

Right now, you can only see the split tasks on the same row when their parent task is collapsed:
In the 7.1 version, the dev team plans to add a way to show subtasks even when the project task is expanded.

Right now, you need to do that by using Gantt API and Javascript. Here are examples of how it can be implemented:
gantt.templates.task_text approach:
addTaskLayer approach:

Thank you very much.

If regular task has more task ,this method shows a problem error.

If you have several tree level, you can use the eachTask method and specify the parent task ID as the second parameter. Then Gantt will iterate all the children of the specified task.
Here is the updated snippet:

In this updated snippet, 09 Apr is no regular task , but the Project #1 showed error.
Is this a bug?

Not, it is not a bug, it is Task #4 which is a subtask of Project #1.
Other subtasks are behind it:

That is expected, as you should all the child tasks on the same line.

The dev team added the Rollup feature:
You can check how it works in the following sample:

Thank you very much for your reminder. I will contact you for the latest documents