Apparently it's a thing to do, when your probation period is over, so would one go about that? A big dinner? Sweets? Drinks?
And also imporant: Who's to be invited for that? The whole company? Your direct colleagues? Your hiring manager and above?
As someone quickly approaching the end of their 6 month prob period, I would say cakes/sweets/treats for the office. If it is a huge office, then for your team and maybe people you've worked with closely/directly during your time there.
Anything bigger than that makes it more of a deal than it is. You expected to survive your prob period (presumably!), they expected you to survive it, so it was expected
As an experienced professional in IT with many years of experience and who has worked at a number of companies small and large, I have never seen a celebration of any sorts for passing a probation. I think most professionals expect to pass a probation and think of it as merely an employer formality. The fact that someone might openly celebrate this would signal to management that this person wasn't expecting to get it and it might be more telling of their work ethic and self-worth than they had previously realized.
If you want to go out to dinner with a friend or family to celebrate quietly that's fine, but I wouldn't bring this up at work at all.
I just passed mine and I work for a team of 6, we all went out for a quiet meal after work, we did how ever let everyone know and if they wanted to join us they could. Primarily was interested in my team, few other people who work there turned up who I would consider friends. I also gave a box of biscuits to my team.
My colleague who passed hers two weeks before me, didn't really do much with us, other than coming in with a hang over the next day..