How to count child node of a tree

GetChildForIDs(List<int> IDs)
{
   List<int> IdsToReturn = new List<int>();
   List<int> LIds = TableRepository.GetAll().where(x=>IDs.Contains(x.ID) & x.ID > 0).select(x=>x.LeftChild).ToList();
   List<int> RIds = TableRepository.GetAll().where(x=>IDs.Contains(x.ID) & x.ID > 0).select(x=>x.RightChild).ToList();
   
   IdsToReturn.AddRange(LIds);
   IdsToReturn.AddRange(RIds); 
   
   if(IdsToReturn.Count()>0)
   {
      GetChildForIDs(IdsToReturn);
      
      //Here Count is Class Level Static Variable
      Count = Count + IdsToReturn.Count();

   }
 
}