  This paper presents a novel unsupervised abstractive summarization method for
opinionated texts. While the basic variational autoencoder-based models assume
a unimodal Gaussian prior for the latent code of sentences, we alternate it
with a recursive Gaussian mixture, where each mixture component corresponds to
the latent code of a topic sentence and is mixed by a tree-structured topic
distribution. By decoding each Gaussian component, we generate sentences with
tree-structured topic guidance, where the root sentence conveys generic
content, and the leaf sentences describe specific topics. Experimental results
demonstrate that the generated topic sentences are appropriate as a summary of
opinionated texts, which are more informative and cover more input contents
than those generated by the recent unsupervised summarization model
(Bra\v{z}inskas et al., 2020). Furthermore, we demonstrate that the variance of
latent Gaussians represents the granularity of sentences, analogous to Gaussian
word embedding (Vilnis and McCallum, 2015).
