Building a tree in python
Please read over PEP 8 as your naming style is unidiomatic, and would cause programmers to be confused when seeing your code in the wild.
I would move getting and setting a node by index into their own functions.
if self.value &gt;= 0 only hinders your code, the value -1 is perfectly valid in binary trees. It also means that you're limiting value to types that can be compared to integers, meaning you can't enter strings.
Using recursion in addNode is a good idea, but I find the non-recursive alternate to be easier to understand.
Your code doesn't care if I enter addNode([0, 2], 1). This seems fishy as if this were a Trinary Tree that would mean something completely different. I recommend raising a ValueError in this case.
Your printTree is pretty good.
I'd change the level argument in printTree to be a keyword argument only. This is because then it's explicit that it's changing the level, and it's something normal code shouldn't accidentally change.
Personally I think if self.left is not None is better here than if self.left, but as Node can't be falsy it doesn't matter too much.
I've added some basic docstrings, defined in PEP 257.
I have also added some typing to your code.
By using typing and mypy I found that addNode can error when the specified path doesn't exist. It would be better in these cases to raise an error telling the user why.
You can use a if __name__ == '__main__': guard to prevent code running on import. This means if you later import this code in another module then the testing code won't run.


from __future__ import annotations

from typing import Any, Optional, Sequence


class Node:
    """Test binary tree."""

    def __init__(
            self,
            value: Any,
            right: Optional[Node] = None,
            left: Optional[Node] = None,
    ):
        """Initialize binary tree, with specified children nodes."""
        self.value = value
        self.right = right
        self.left = left

    def _get_index(self, index: int) -&gt; Optional[Node]:
        """Get node via integer index."""
        if index == 0:
            return self.left
        elif index == 1:
            return self.right
        else:
            raise ValueError(f'Invalid index {index}')

    def _set_index(self, index: int, value: Node) -&gt; None:
        """Set node via integer index."""
        if index == 0:
            self.left = value
        elif index == 1:
            self.right = value
        else:
            raise ValueError(f'Invalid index {index}')

    def add_node(self, parents: Sequence[int], value: Node) -&gt; None:
        """Add the provided node to the tree."""
        node: Optional[Node] = self
        for index in parents[:-1]:
            if node is not None:
                node = node._get_index(index)
        if node is None:
            raise ValueError("Parent node doesn't exist.")
        node._set_index(parents[-1], value)

    def add_value(self, parents: Sequence[int], value: Any) -&gt; None:
        """Add the provided value to the tree."""
        self.add_node(parents, Node(value))

    def print_tree(self, *, level: int = 0) -&gt; None:
        """Print the tree."""
        print('  ' * level + str(self.value))
        for child in (self.left, self.right):
            if child is not None:
                child.print_tree(level=level + 1)


if __name__ == '__main__':
    tree = Node(0)
    tree.add_value([0], 1)
    tree.add_value([1], 1)
    r"""
    Graph looks like
       0
      / \
     1   1
     """

    tree.add_value([0, 0], 3)
    tree.add_value([0, 1], 8)
    tree.add_value([1, 0], 4)
    tree.add_value([1, 1], 7)
    r"""
    Graph looks like
               0
             /   \
            1      1
           / \    / \
          3  8    4  7
    """
    tree.print_tree()