I want to say that "a sense of belonging" cannot be inspired by a 10th anniversary celebration! The sense of belonging is the inevitable product of the trust, help, education, etc. accumulated by the company to its employees every day, every hour, and every moment.
But I still want to give you some personal suggestions:
1. You can get some photos or videos of past employees (those who are still working are best)
2. Let a person with enough weight in the company (general manager or chairman) present awards to a few ordinary old employees (who should be loyal to the company, never give up, and have good quality) at the celebration. (For example, "Years of Dedication Award", etc.)
3. Announce some exciting good news (of course it must be closely related to the interests of employees)
That's all I have thought about for the time being! In fact, you know how this sense of belonging is formed in a day! If you don't do it right, it will be self-defeating. I personally feel that these three small aspects I mentioned are relatively safe! Hope this helps!