I have a cd that I am adding to Itunes and it has come up with two separate cds even though they are the same album

I have imported albums into itunes. Every album that has more than one disc has imported correctly. What I mean by this is the discs group together by album. However one of the albums has not done this correctly and I can't see how to correc it. I have checked everything and it all seems ok

Many Thanks

Bodi