class BTNode:
    """Binary Tree node."""

    def __init__(self: 'BTNode', data: object,
                 left: 'BTNode'=None, right: 'BTNode'=None) -> None:
        """Create BT node with data and children left and right."""
        self.data, self.left, self.right = data, left, right

    def __repr__(self: 'BTNode') -> str:
        """Represent this node as a string."""
        return ('BTNode(' + str(self.data) + ', ' + repr(self.left) +
                ', ' + repr(self.right) + ')')

    def is_leaf(self: 'BTNode') -> bool:
        """Is this node a leaf?"""
        return node and not self.left and not self.right