What is the GTD app for iOS with a tree of sub-projects?

Advise please a subject.

As similar software by the usual request, "gtd" in the appstore throws out a whole bunch, just to clarify the criteria:
1. more or less strict adherence to the GTD process, not just a painted tasklist;
2. built-in calendar or integration with iOS-native native;
3. the most important thing! - sub-projects.

I.e. I need the project tree.

A nice bonus would be to sync with any web service. Within 1K rubles are not price is important.
At the moment my criteria is suitable Toodledo, but it willigly client design; I bought it, tried to use it, but realized that I'm not going to deliver pleasure, and therefore, to use them I will not. Here, looking for analogues.

Thanks in advance for the advice. The software, which I will eventually install, be sure to note how the solution.
September 26th 19 at 06:34
3 answers
September 26th 19 at 06:36
todoist do not scales (stupidly not collapsed node of the tree), and there was nothing but sub-projects. But visually a very good course. - Emory41 commented on September 26th 19 at 06:39
September 26th 19 at 06:38
Once used "Priorities". The tree will be there, the calendar at that time was not. There is also a web version.
September 26th 19 at 06:40
Also looking for software with similar functionality, but not found. Projects prefer to work in OmniFocus, but there's no calendar. With the calendar, I guess there's only Calendars and Fantastical, but these applications are more for the average user.

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