Illustration of an example of merger tree reconstruction. Starting from galaxy “a” at z = 4.5 (snap = 041), its progenitors at the previous snapshot are “b” and “c”. Merger trees have been reconstructed all simulated galaxies at z = 4.5 with masses of M_⋆ ≥ 10¹⁰ M_⊙, up to z = 5.1 (snap = 035). This allows us to reconstruct the mass assembly history of the simulated galaxies, identifying those systems that undergo major mergers, defined as galaxy interactions where the relative stellar mass ratio of the merging pair is 1 < μ_⋆ < 4 (see text).