class_docstr: A single linkage format dendrogram tree, with plotting functionality
  and networkX support.
  
  Parameters
  ----------
  linkage : ndarray (n_samples, 4)
      The numpy array that holds the tree structure. As output by
      scipy.cluster.hierarchy, hdbscan, of fastcluster.
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docstr: Return a numpy array representation of the single linkage tree.
  
  This representation conforms to the scipy.cluster.hierarchy notion
  of a single linkage tree, and can be used with all the associated
  scipy tools. Please see the scipy documentation for more details
  on the format.
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code: def to_numpy(self):
      """Return a numpy array representation of the single linkage tree.
  
      This representation conforms to the scipy.cluster.hierarchy notion
      of a single linkage tree, and can be used with all the associated
      scipy tools. Please see the scipy documentation for more details
      on the format.
      """
      return self._linkage.copy()
  
imports: import numpy
  from scipy.cluster.hierarchy import dendrogram
  from sklearn.manifold import TSNE
  from sklearn.decomposition import PCA
  from sklearn.metrics import pairwise_distances
  from warnings import warn
  from ._hdbscan_tree import compute_stability, labelling_at_cut, recurse_leaf_dfs
label_desc: Use image node_id 3 for calling the SingleLinkageTree obj's underlying member method code with example usage: obj.to_numpy() and returns: self