My advisor used my research idea and wrote a paper with another student, what should I do? I had an idea of using a specific type of data in a specific research area (sorry, I realize this sounds vague). No one has used this type of data in this area before. I shared the idea with my advisor. Recently I noticed the advisor and another student published a paper based on my idea. I think it is not fair. What do I do?

Edit: Thank you all for the comments and answers.
To clarify a couple of things: it wasn't just a fleeting conversation or group brainstorming. I came up with the idea myself, did initial work, and shared it with the advisor. I would expect to be at least told they wanted to work on this even if they were to conduct an independent analysis. I do not think the time frame and other factors would allow forgetting where the idea came from. The group works on several topics and my idea was more like a side line project. There is a lot of publications coming from these main topics, so it's not like this specific paper would be crucial for future funding.
I think the worst in the whole situation is that now I distrust my advisor.
It's not clear whether you are still in the same research group. I suspect not, or you would have been aware that another person in the group was doing the work and paper. While it is morally questionable to use someone else's idea without asking them to be involved, there's nothing you can do in the sense of 'getting it fixed'.

But it may be worthwhile sending an email that is not accusing. The adviser may have felt that you were fully occupied, or that the project was too easy for you but was a good training project for a student, or simply forgotten about the conversation or any number of other reasons. An email like:

Dear Prof X - I saw your recent paper Y. As you may remember from our discussion (approximate time frame), I am interested in this idea and the paper looks very similar to what we discussed. I am disappointed not to be involved in the implementation so far and would like to participate in any future work coming out of this paper.