def has_allowed_extension(name, allowed_file_endings=None):
    if not allowed_file_endings:
        return True
  
    return any(name.endswith(file_ending) for file_ending in allowed_file_endings)

def collect_nested_files(directory_path, forbidden_dir_names=None, allowed_file_endings=None, collected_paths=None):
    if forbidden_dir_names is None:
        forbidden_dir_names = ['env', '.git', '__pycache__', 'server']
        
    if allowed_file_endings is None:
        allowed_file_endings = ['.md']
        
    if collected_paths is None:
        collected_paths = (directory_path, [])

    if any(name in directory_path.split(os.path.sep) for name in forbidden_dir_names):
        return collected_paths
      
    subpaths = collected_paths[1]
  
    nested_list = sorted(os.listdir(directory_path))

    for name in nested_list:
        nested_path = os.path.join(directory_path, name)
      
        if os.path.isdir(nested_path):
            nested_dir = collect_nested_files(nested_path, collected_paths=(nested_path, []))
            if nested_dir[1]:
                subpaths.append(nested_dir)
        else:
            if not has_allowed_extension(name, allowed_file_endings=allowed_file_endings):
                continue
            subpaths.append(nested_path)
  
    return collected_paths