Please don't include it as its own bucket.
There's two approaches here:
First, as Vlad mentioned, you can incorporate it into an existing bucket. Implementation is a great example (as its riddled with risks).
Second you can simply incorporate it as you speak. I.e. If we're looking at market entry, you may have a bucket for the attractiveness of the Market as a whole, Our company in this market (how it might far), and then how to do it.
For #1 "Market as a whole", obviously you mention any environmental, economic, or political risks. Anything possibly negative about the market is inherently a risk
For #2 "Our company/product", If we've never expanded before that's a risk. If we're low on $ that's a risk. If our product is totally new/untested, that's a risk. And so on and so forth.
For #3 "How", an acquisition is risky because of $ and integration, organic growth is risky because of time and lack of local market knowledge, a partnership is risky because of lack of control.
Make sense? When analysing any problem the risks are inherent in your analysis...they're not a seperate bucket!