  Using mean-field theory and high resolution Monte Carlo simulation technique
based on multi-histogram method, we have investigated the critical properties
of an antiferromagnetic XY model on the 2D Kagom\'e lattice, with single ion
easy-axes anisotropy. The mean-field theory predicts second-order phase
transition from disordered to all-in all-out state for any value of anisotropy
for this model. However, Monte Carlo simulations result in first order
transition for small values of anisotropy which turns to second order with
increasing strength of anisotropy, indicating the existence of a tricritical
point for this model. The critical exponents, obtained by finite-size scaling
methods, show that the transition is in Ising universality class for large
values of anisotropy, while the critical behaviour of the system deviates from
2D-$\phi^6$ model near the tricritical point. This suggests the possibility for
existence of a new tricritical universality in two-dimensions.
