3-methyl hex-2-ene CH3CH=C(CH3)CH2CH2CH3 has a methyl group either side of the double bond and has geometric isomers with both CH3 groups on the same side (cis), or trans to the d.b.
4-methyl hex-3-ene CH3CH2CH=C(CH3)CH2CH3 has an ethyl group either side of the double bond and has geometric isomers with both C2H5 groups on the same side (cis), or trans to the d.b.