Which orbitals on overlapping will form $\sigma$ and $\pi$ bond in $C=C$ of alkene? Explain.

(N/A) In an alkene,each carbon atom undergoes $sp^{2}$ hybridization.
The $\sigma$-bond between the two carbon atoms is formed by the head-on (axial) overlapping of one $sp^{2}$ hybrid orbital from each carbon atom.
The $\pi$-bond is formed by the lateral (sideways) overlapping of the unhybridized $2p$ orbitals of the two carbon atoms,which are parallel to each other and perpendicular to the molecular plane.