code: def get_tissue_in_references(self, entry):
          
          tissue_in_references = []
          query = "./reference/source/tissue"
          tissues = {x.text for x in entry.iterfind(query)}
  
          for tissue in tissues:
  
              if tissue not in self.tissues:
                  self.tissues[tissue] = models.TissueInReference(tissue=tissue)
              tissue_in_references.append(self.tissues[tissue])
  
          return tissue_in_references
docs: get list of models.TissueInReference from XML node entry
  
          :param entry: XML node entry
          :return: list of :class:`pyuniprot.manager.models.TissueInReference` objects