It organizes things by the spawning greenlet, if possible.

Example output::

```
<greenlet.greenlet object at 0x10753a9b0>
 :    Running:
 :      File "/tmp/t.py", line 38, in <module>
 :        print("\n".join(format_run_info()))
 :      File "//src/gevent/util.py", line 99, in format_run_info
 :        _format_greenlet_info(lines)
 :      File "//src/gevent/util.py", line 132, in _format_greenlet_info
 :        lines.extend(tree.format_lines(details=True))
 :      File "//src/gevent/util.py", line 265, in format_lines
 :        for l in self._render(tree)]
 :      File "/-main/src/gevent/util.py", line 310, in _render
 :        self.__render_tb(tree, 'Running:', self.greenlet.gr_frame)
 :      File "//src/gevent/util.py", line 281, in __render_tb
 :        tb = ''.join(traceback.format_stack(frame))
 :    Greenlet Locals:
 :      Local <type 'gevent._local.local'> at 0x10759cec0
 :        {'foo': 42}
 +--- <Greenlet "Greenlet-0" at 0x107405cb0: _run>; finished with value <Greenlet "Greenlet-4" at 0x10
 :          Parent: <Hub at 0x10753a550 select default pending=0 ref=0>
 :          Spawned at:
 :            File "/tmp/t.py", line 1, in <module>
 :              from gevent.util import GreenletTree
 |    +--- <Greenlet "Greenlet-4" at 0x10780b260: _run>; finished
 :                Parent: <Hub at 0x10753a550 select default pending=0 ref=0>
 :                Spawned at:
 :                  File "/tmp/t.py", line 1, in <module>
 :                    from gevent.util import GreenletTree
 :                  File "/tmp/t.py", line 12, in t2
 :                    def t2():
 +--- <Hub at 0x10753a550 select default pending=0 ref=0>
 :          Parent: <greenlet.greenlet object at 0x10753a9b0>
 :          Running:
 :            File "/Users/jmadden/Projects/GithubSources/gevent-main/src/gevent/hub.py", line 673, in run
 :              loop.run()
 +--- <Greenlet "Greenlet-1" at 0x10780b368: _run>; finished with value <Greenlet "Greenlet-5" at 0x10
 :          Parent: <Hub at 0x10753a550 select default pending=0 ref=0>
 :          Spawned at:
 :            File "/tmp/t.py", line 1, in <module>
 :              from gevent.util import GreenletTree
 |    +--- <Greenlet "Greenlet-5" at 0x10780b578: _run>; finished
 :                Parent: <Hub at 0x10753a550 select default pending=0 ref=0>
 :                Spawned at:
 :                  File "/tmp/t.py", line 1, in <module>
 :                    from gevent.util import GreenletTree
 :                  File "/tmp/t.py", line 12, in t2
 :                    def t2():
 +--- <Greenlet "Greenlet-2" at 0x10780b470: _run>; finished with value <Greenlet "Greenlet-6" at 0x10
 :          Parent: <Hub at 0x10753a550 select default pending=0 ref=0>
 :          Spawned at:
 :            File "/tmp/t.py", line 1, in <module>
 :              from gevent.util import GreenletTree
 :          Spawn Tree Locals
 :          {'stl': 'STL'}
 |    +--- <Greenlet "Greenlet-6" at 0x10780b680: _run>; finished with value <Greenlet "Greenlet-7" at 0x10
 :                Parent: <Hub at 0x10753a550 select default pending=0 ref=0>
 :                Spawned at:
 :                  File "/tmp/t.py", line 1, in <module>
 :                    from gevent.util import GreenletTree
 :                  File "/tmp/t.py", line 21, in t3
 :                    def t3():
 |         +--- <Greenlet "Greenlet-7" at 0x10780b788: _run>; finished
 :                      Parent: <Hub at 0x10753a550 select default pending=0 ref=0>
 :                      Spawned at:
 :                        File "/tmp/t.py", line 1, in <module>
 :                          from gevent.util import GreenletTree
 :                        File "/tmp/t.py", line 21, in t3
 :                          def t3():
 :                        File "/tmp/t.py", line 12, in t2
 :                          def t2():
 +--- <Greenlet "Greenlet-3" at 0x10780b890: _run>; finished with value [<gevent.util.GreenletTree obj
            Parent: <Hub at 0x10753a550 select default pending=0 ref=0>
            Spawned at:
              File "/tmp/t.py", line 1, in <module>
                from gevent.util import GreenletTree
```