Assuming you didn’t mean “expand the section,” you can somehow request this of Asana but it’s unlikely to be done, I think, because the subtask behaves as a top-level tass without subtasks itself, and so there’s no associated expand/collapse icon for it.
FYI you can accomplish this with a Flowsana rule: the rule would be “When a new task is created, add it to project [the current project where the rule is being created]” and you would select to have this rule apply only to subtasks, which is an available option in Flowsana.
This feature would increase Asana’s pitch for encouraging users to upgrade to the Business plan as automatically attaching subtasks to a project would hopefully allow for users to better utilize the workload and goals features. Currently both the workload and goals do not capture data presented by sub-tasks. Having this feature would provide a more accurate view of a team member’s workload without having to go through all the clicks to add a project to a sub-task (which creates task duplication by creating a task on the project). It also would provide for a more accurate picture of progress made towards goals.