In Chrome, click the 3 dots at the top right of the chrome://bookmarks page, and export your bookmarks as an HTML file.
Then, in Opera, goto the URL opera://settings/importData, select "Bookmarks HTML file" in the drop-down, and import the HTML file. Then, at the opera://bookmarks page, you can select and move anything that's not in the right place to the right place.
As for importing directly from Opera, I think the import wizard just chooses the "Default" profile with no way to pick a different one.