title: OSMNX : How to plot nodes only?
body: <p>I've tried to plot a map with trees. These are nodes in openstreetmap so I'm wondering if it's possible to plot a map with nodes only, without edge between them ?</p>
  
  <p>Here's my code:</p>
  
  <pre><code>place=['Saint-Egreve,France']
  G = ox.graph_from_place(place,retain_all=True,truncate_by_edge=True,simplify=False, network_type='none',infrastructure='node[natural=tree]')
  fig, ax = ox.plot_graph(ox.project_graph(G))
  </code></pre>
  
  <p>Returning error :</p>
  
  <pre><code>Traceback (most recent call last):
    File "./test.py", line 102, in &lt;module&gt;
      fig, ax = ox.plot_graph(ox.project_graph(G))
    File "/home/syl20/.conda/envs/ox/lib/python3.8/site-packages/osmnx/plot.py", line 362, in plot_graph
      west, south, east, north = edges.total_bounds
    File "/home/syl20/.conda/envs/ox/lib/python3.8/site-packages/pandas/core/generic.py", line 5274, in __getattr__
      return object.__getattribute__(self, name)
    File "/home/syl20/.conda/envs/ox/lib/python3.8/site-packages/geopandas/base.py", line 523, in total_bounds
      return GeometryArray(self.geometry.values).total_bounds
    File "/home/syl20/.conda/envs/ox/lib/python3.8/site-packages/pandas/core/generic.py", line 5274, in __getattr__
      return object.__getattribute__(self, name)
    File "/home/syl20/.conda/envs/ox/lib/python3.8/site-packages/geopandas/geodataframe.py", line 101, in _get_geometry
      raise AttributeError(
  AttributeError: No geometry data set yet (expected in column 'geometry'.
  </code></pre>
  
  <p>Thank you for your precious help !</p>
  
  <p>Sylvain</p>