  The two--neutron separation energy of $^6$He has been reproduced for the
first time in a realistic parameter--free microscopic multicluster model
comprising the $\alpha +n+n$ and $t+t$ clusterizations, with $\alpha$ cluster
breathing excitations included. The contribution of the $t+t$ channel is
substantial. A very thick (0.85 fm) neutron halo has been found in full
agreement with the results of the latest phenomenological analysis.
