  We report on the high statistics two-pion correlation functions from pp
collisions at $\sqrt{s}=0.9$ TeV and $\sqrt{s}$=7 TeV, measured by the ALICE
experiment at the Large Hadron Collider. The correlation functions as well as
the extracted source radii scale with event multiplicity and pair momentum.
When analyzed in the same multiplicity and pair transverse momentum range, the
correlation is similar at the two collision energies. A three-dimensional
femtoscopic analysis shows an increase of the emission zone with increasing
event multiplicity as well as decreasing homogeneity lengths with increasing
transverse momentum. The latter trend gets more pronounced as multiplicity
increases. This suggests the development of space-momentum correlations, at
least for collisions producing a high multiplicity of particles. We consider
these trends in the context of previous femtoscopic studies in high-energy
hadron and heavy-ion collisions, and discuss possible underlying physics
mechanisms. Detailed analysis of the correlation reveals an exponential shape
in the outward and longitudinal directions, while the sideward remains a
Gaussian. This is interpreted as a result of a significant contribution of
strongly decaying resonances to the emission region shape. Significant
non-femtoscopic correlations are observed, and are argued to be the consequence
of "mini-jet"-like structures extending to low $p_{\rm T}$. They are well
reproduced by the Monte-Carlo generators and seen also in $\pi^+\pi^-$
correlations.
