The physical mechanism(s) leading to the origin of the extended Main Sequence Turn Off (eMSTO) in the Galactic open star clusters is currently one of the fascinating research topics. The theories explaining the presence of the eMSTO in the open clusters are still emerging, and keen attention is needed to develop an in-depth understanding of its origin. We comprehensively analyze the eMSTO present in the open cluster NGC 2355. We utilize spectra from the Gaia-ESO surveys’ archives to estimate the stars’ atmospheric parameters and projected rotational velocity, v sin i. We find that the red part of the eMSTO is preferentially occupied by fast-rotating stars with a mean v sin i value of 135.3±4.6 km/s, whereas blue eMSTO hosts slow-rotating stars with an average v sin i equal to 81.3±5.6 km/s. This suggests the presence of the eMSTO in NGC 2355 is possibly related to the spread in rotation rates of stars. The tidal interaction theory explaining the spread in rotation rates proposes that all the eMSTO stars were initially fast-rotating until tidal locking in the binaries caused some stars to slow down. Another hypothesis suggests that the star-disc interaction during the pre-main-sequence (PMS) phase may cause the spread in the rotation rates of the eMSTO stars. We use synchronization time and spatial distribution of the eMSTO stars to investigate the most likely mechanism responsible for the presence of the eMSTO in the cluster. Based on our analysis of the results, we conclude that the star-disc interaction in the PMS phase of the stars is the most likely reason for the origin of the eMSTO in NGC 2355. In the talk, I will discuss these results and their physical interpretation in detail to address the critical questions currently at the forefront of eMSTO research.