Personally, I would pick 1. To have all bookmarks (from all tabs) in a treeview is not as intuitive as showing the bookmarks for the current file/tab. qpdfview seems to be a light-weight PDF viewer, so it doesn't seem necessary to add a feature for cross-referencing. Having a tree view is also more programming work, and I don't think the benefit is enough--it's quite small for my use-cases (but maybe other people have other use-cases to me).
To have all bookmarks available implies that the user would be switching back and forth between this file and that. If it was me, if I needed to check a bookmark in another document, I'd just switch between tabs (it's not hard with Ctrl+Tab).
Personally, I would pick 1. To have all bookmarks (from all tabs) in a treeview is not as intuitive as showing the bookmarks for the current file/tab. qpdfview seems to be a light-weight PDF viewer, so it doesn't seem necessary to add a feature for cross-referencing. Having a tree view is also more programming work, and I don't think the benefit is enough--it's quite small for my use-cases (but maybe other people have other use-cases to me).
To have all bookmarks available implies that the user would be switching back and forth between this file and that. If it was me, if I needed to check a bookmark in another document, I'd just switch between tabs (it's not hard with Ctrl+Tab).
Thank you for your work.