code: def write_bed_with_trackline(bed, out, trackline, add_chr=False):
      
      df = pd.read_table(bed, index_col=None, header=None)
      bt = pbt.BedTool('\n'.join(df.apply(lambda x: '\t'.join(x.astype(str)), 
                                          axis=1)) + '\n',
                       from_string=True)
      if add_chr:
          bt = add_chr_to_contig(bt)
      bt = bt.saveas(out, trackline=trackline)
docs: Read a bed file and write a copy with a trackline. Here's a simple trackline
      example: 'track type=bed name="cool" description="A cool track."'
  
      Parameters
      ----------
      bed : str 
          Input bed file name.
      out : str
          Output bed file name.
      trackline : str
          UCSC trackline.
      add_chr : boolean
          Add 'chr' to the chromosomes in the input file. Necessary for
          UCSC genome browser if not present.