Ten years (of) experience

10+ years of experience is proper. Units of time like years can also be used in a possessive sense, so you can also say 10+ years' experience. See this question and this question for more details about that.

In formal writing you should not use 10+ years experience without the apostrophe, but then you would not normally say "10+" in normal writing either. Résumé writing is a bit informal and has conventions of its own, such as frequent omission of articles and first person pronouns ("Implemented process that increased efficiency of widget production by 400 percent"). So you might be able to get away with years experience in that context. Still, you can't go wrong if you get it right: stick with either years of experience or years' experience.

You certainly may include the “of” and so indicate that experience is a thing of which you have a certain quantity, namely (more than) ten years. An alternative is to write “10+ years’ experience,” which actually turns the possessive or genitive relation completely around: if we were to reconvert the possessive “years’ ” into periphrastic genitive with “of,” we would wind up with the experience of more than ten years, rather than more than ten years of experience. But it is remarkable how very little difference in meaning that makes.