The structure have been shown in the image attached to this answer.
How do we know the aldehyde functional group ?
The aldehyde functional group, often represented by the symbol -CHO, is defined as having a carbonyl group (C=O) bound to a hydrogen atom. The carbonyl carbon is directly connected to two hydrogen atoms and another carbon or hydrogen atom in a structural formula.
Look for the distinctive C=O bond and the existence of a hydrogen atom that is directly attached to the carbonyl carbon in the molecular structure to determine the presence of the aldehyde functional group.