  Topological insulators are known to their metallic surface states, a result
of strong-spin-orbital coupling, that show unique surface transport phenomenon.
But these surface transports are buried in presence of metallic bulk
conduction. We synthesized very high quality Bi$_2$Te$_2$Se single crystals by
modified Bridgman method, that possess high bulk resistivity of
$>$20~$\Omega$cm below 20~K, whereas the bulk is mostly inactive and surface
transport dominates. Temperature dependence resistivity follows the activation
law like a gap semiconductor in temperature range 20-300~K. We designed a
special measurement geometry, which aims to extract the surface transport from
the bulk. This special geometry is applied to measure the resistance and found
that Bi$_2$Te$_2$Se single crystal exhibits a cross over from bulk to surface
conduction at 20~K. Simultaneously, the material also shows strong evidence of
weak anti-localization in magneto-transport due to the protection against
scattering by conducting surface states. This novel simple geometry is an easy
route to find the evidence of surface transport in topological insulators,
which are the promising materials for future spintronic applications.
