Hi Ravi, there are a lot of treks around Manali but they would be closed during the time you are planning your visit because of snow. Manali receives a lot of snow and December-Janaury is the peak winter time. You can try easier treks Around Kasol and Kullu region, like Kheerganga, Malana trek or Parashar lake trek. They are comparatively shorter trek but they would be accessible during that time of the year.