code: def mean_oob_mae_weight(trees):
          
          weights = []
          active_trees = []
          for tree in trees:
              oob_mae = tree.out_of_bag_mae
              if oob_mae is None or oob_mae.mean is None:
                  continue
              weights.append(oob_mae.mean)
              active_trees.append(tree)
          if not active_trees:
              return
          weights = normalize(weights)
          return zip(weights, active_trees)
docs: Returns weights proportional to the out-of-bag mean absolute error for each tree.