An alkene monomer has the formula CH2=C(CH3)CH2CH3\text{CH}_2{=}\text{C}(\text{CH}_3)\text{CH}_2\text{CH}_3CH2=C(CH3)CH2CH3.
A student proposes that its addition polymer has the repeating unit [-CH(CH3)-CH(CH2CH3)-]n\left[\text{-CH}(\text{CH}_3)\text{-CH}(\text{CH}_2\text{CH}_3)\text{-}\right]_n[-CH(CH3)-CH(CH2CH3)-]n.
Explain why the proposed repeating unit is incorrect. Give the correct repeating unit.