In a grouped list, how to display items of an intersection of two groups

Provided I have a category which gives x non mutually exclusive options. I have a list of items which can be tagged with several of these mutually non exclusive options.

• Item 1
  • Group A
• Item 2
  • Group B
• Item 3
  • Group A + B
• Group C ...

A user can now select one/several of the options so they retrieve a list of items according to each options they selected and the union of these options, if needed.

• Group A -- selected
• Group B -- selected
• Group C

I have a constraint when it comes to displaying the result: the items must be grouped under the options they are tagged with.

• Group A
  • Relevant items
• Group B
  • Relevant items

This is where I am faced with a choice to make in order to display the items which are tagged with several of the select options - hence are at the intersection of several groups.

The alternatives are: display each items several times, one under each group they belong to, like so:

• Group A
  • Item 1
  • Item 3
• Group B
  • Item 2
  • Item 3

Or display a group for each intersection of groups

• Group A
  • Item 1
• Group B
  • Item 2
• Group A + B
  • Item 3

Solution 1 result in a duplication of the content (the item), solution 2, a duplication of the meta-information (the categories).

Now, this was an imaginary explanation. My real case implies 5 categories each with between 3-5 options and two nested grouping based on 2 of these categories. As a result, whichever solution comes with a big overload of duplicated information - just think of the possible combination of groups. Nonetheless, I would like to have your opinions and knowledge on which would be the worse of two evils out of these two solutions ?

I might add that the value proposition I am working with for this content is partly, the number of items of content. Hence, albeit being more readable, I believe that solution 1 could be perceived as bearing disingenuity as it increase that number. Solution 2 would be worse in terms of readability though.

Of course, I am also investigating alternatives to grouping altogether but would like to put this problem out there for reflexion and see if someone comes with different angles than mine.