Return the sum of the distance between self and ancestor
Parameters:  ancestor : TreeNode


Returns:  float

Raises:  NoParentError
NoLengthError

See also
Examples
>>> from six import StringIO
>>> from skbio import TreeNode
>>> tree = TreeNode.read(StringIO("((a:1,b:2)c:3,(d:4,e:5)f:6)root;"))
>>> root = tree
>>> tree.find('a').accumulate_to_ancestor(root)
4.0