This is a matter of property. If you're working with a PI, then that means that you're most likely using resources from that PI's lab to gather your data and analyze it. That PI, in turn, is funded by specified funding agencies that must acknowledged in any scientific work. So you cannot present data without your PI's permission.
Second, it's not necessarily in your best interest to present the data anyway. Any time you present data at a conference, you have to be mindful that you might get scooped on it and you don't want to end up in a position where you don't get a publication because someone saw your ideas at the conference and got on it before you finished. I know of PIs who will attend these conferences, get ideas, and then get huge teams of grad students to work on the projects to finish very quickly and scoop other people. They can do this because they have huge labs and thus many resources to expend whereas the other PI might have less funding and a smaller lab and so must work at a slower pace. This is why PIs often embargo graduate theses - they don't want information getting out before they're ready to publish.