If you have ever sent any amount from the wallet you probably have a change address. These are called "internal" addresses which do not show in the trezor interface. The only way you can find this out is by using the pubx id and inputting it into a block explorer. If the amount matches then it is a change address. These are automatically handled by trezor and is normal behavior. You can find the public key in your receive tab. Go onto it and you will need to click "reveal key". The public key is safe to copy and safe to give to people but it does have privacy issues because if you give it to some one they can track your whole transaction history but you are probably not concerned because you already have put 1 address into the explorers.