  The non-identical particle femtoscopy is a technique that is developed to
estimate the dimension of a particle-emitting medium as well as the average
pair-emission asymmetry between the particles using two-particle correlation
functions. The analysis of femtoscopic correlations for all possible charged
combinations of pion-kaon pairs in Pb$-$Pb collisions at
$\sqrt{s_{\mathrm{NN}}}=$ 5.02 TeV with ALICE at the LHC is presented in this
article. The results are extracted for different centrality classes of Pb$-$Pb
collisions using the spherical harmonics representations of the correlation
functions, $C^{\rm 0}_{\rm 0}$ and $Re C^{\rm 1}_{\rm 1}$. The evolution of the
femtoscopic parameters with multiplicity and collectivity of the system is
discussed extensively. The femtoscopic parameters are observed to increase with
the multiplicity. The non-zero values of pair-emission asymmetry and the
decrease of source-size with increasing pair-transverse momentum indicate the
presence of collectivity in the system.
