What is the best position for a submenu in a page with a sidebar?

I'm currently working on a project in which navigation positioning is key for the UX flow of the user. I've been trying several options, but I'm not sure I've found a solution that captivates the right understanding from the user.

I've got a layout in which the navigation is a sidebar and each item contains a submenu. By default, the first item would be selected, once you dive in the page. Selecting other items in this submenu would change the meaning of the content on the page. As if the content maintained the same context, but changed focus.

Now, the issue is: between option A and B, which do you think is the most intuitive and easy to understand in this situation and why?

enter image description here

  • A - contains the menu on the sidebar on the left (blue) and the submenu horizontally displayed on the top of the page on the right (green).
  • B - contains the menu on the sidebar on the left (blue) and the submenu is displayed vertically below each parent menu item (green).
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