The boiling point of esters increases with molecular weight (and therefore, number of carbon atoms) because of more dispersion forces. But if you had two different esters with the same number of carbon atoms but different structures (e.g. methyl-ethanoate and ethyl-methanoate), what determines which one will have a higher boiling point? Does it have something to do with the number of carbon atoms in the alkyl group in comparison to the acyl group?
In this case you have consider the degree of branching of the isomer, this influences the strength of intermolecular forces. Think of how tree logs with lots of branches sticking out cannot stack together with each other as easily as a pile of logs with no branches. Branched chain isomers have less contact and therefore weaker intermolecular forces and lower boiling point and straight chained isomers have better contact and thus stronger molecular forces and higher boiling point.