Investigate why EFDT trees with different number of nodes have a similarity score of 100%

[anjsimmo]

In some cases, EFDT trees with different numbers of nodes have a similarity score of 100%. Also, in the conversion of EFDT trees to a ruleset, both <= and > branches are shown as <=

See the following notebook for a demonstration of the issue: https://github.com/a2i2/tree_diff/blob/re-evaluation/notebooks/Similarity%20Score%20Issues%20-%20Wrong%20results%20for%20EFDT%20trees.ipynb