Bug fix: Failure to remove nodes that introduce a loop in the tree.

[MogomotsiFM]

The code fails with the following exception: ValueError: The truth value of a DataFrame is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().

This is because the test for equality is not defined for DataFrame objects. As a result, the nodes resulting in a loop are not removed and the tree is invalid.

The following is the test case that fails:

tree = Tree()
tree.condition(output=Action(value=100), condition="SubA")
tree.condition(output=Action(value=200), condition="SubB")
try:
    tree.include_subtree(tree)
except Exception as e:
    print(e)

To solve this, we note that the addresses of nodes are used to detect loops. As a result, we use these addresses to select nodes that must be removed. The proposed solution is at this branch: https://github.com/MogomotsiFM/dsp-decision-engine/tree/loop-causes