There's a reason why the phrase "great minds think alike" has become cliché -- it happens a lot.   Over time, as your Brainstorm becomes filled with hundreds or thousands of ideas, some of them are bound to overlap.

The question is: what's the best way to handle these overlapping ideas?

The first reaction most people have is to "merge" the ideas.  We caution against this reaction based on our experience with managing innovation at Intuit and with our customers.  Jumping too quickly to "merge" ideas runs the risk of missing out on the nuanced differences between the two ideas and any value that could result.  To make that more clear here's a concrete, albeit exaggerated, example:

Two teams are toiling away on an idea for a new product.  Each has the idea for creating incandescent light through the process of running an electric current through a filament contained within an evacuated glass bulb... 

Now, if this was happening in your organization, you could say that having two teams pursue the same idea is an inefficient allocation of resources.  You could remove this inefficiency by shutting down the team you feel is not on the right path or by merging the teams together and having them pursue the most promising path.  But, doing so may shut your organization out from potentially valuable aspects of the idea:

As it turns out, the two teams vary slightly in one aspect of their idea -- the filament.  One team has discovered that using a carbonized bamboo filament boosts the lifetime of their incandescent light to 1,200 hours.  This boost is significant because it makes the incandescent light commercially viable.

As you've probably guessed, the team with the 1,200 hour light was headed by Thomas Edison.  The other team was headed by Joseph Wilson Swan (you can read more about this story on Wikipedia).  Now, these guys were obviously not using Brainstorm in the late 1800s, but the point about how ideas turn into successful innovations is valid.  What's valuable to an organization is not necessarily the idea itself, but the nuanced understanding of the problem and potential solutions that emerge from collaboration around the idea.  As a result, it's potentially dangerous to "merge" ideas based on a shallow understanding of what the ideas are about because you can lose that nuanced understanding.

That's why we bias Brainstorm towards connecting related ideas together as opposed to eliminating "duplication."  The truth is, it's very rare that two ideas are complete duplicates of each other.  The light bulb example above would be considered "duplicate ideas" in most innovation management systems.  But, the nuanced difference in approach to the filament was the difference between Thomas Edison being known as the most famous American innovator and Joseph Wilson Swan being a footnote in history.  Nuances can be critical.  In Brainstorm's context, what's most important is that the two ideas are aware of each others' existence and have a conversation about how best to proceed.   Then, they can make an informed decision about whether to eliminate duplication, merge the efforts, or proceed separately.

If you want to merge ideas...

In the case of your Brainstorm ideas, if the decision is to proceed separately, then nothing needs to be done.  If the decision is to eliminate duplication or merge the efforts, you can take the following steps:

1. Choose which of the similar ideas should become the primary idea
2. Move any relevant content from the secondary idea to the primary idea (copy/paste content from notes, invite team members, etc.)
3. Remove the content from the secondary idea
4. Add a note at the top of the secondary idea with a link to the primary idea (see picture below)