  The precision of the parallax measurements by Gaia is unprecedented. As of
Gaia Data Release 2, the number of known nearby open clusters has increased.
Some of the clusters appear to be relatively close to each other and form
aggregates, which makes them interesting objects to study. We study the
aggregates of clusters which share several of the assigned member stars in
relatively narrow volumes of the phase space. Using the most recent list of
open clusters, we compare the cited central parallaxes with the histograms of
parallax distributions of cluster aggregates. The aggregates were chosen based
on the member stars which are shared by multiple clusters. Many of the clusters
in the aggregates have been assigned parallaxes which coincide with the
histograms. However, clusters that share a large number of members in a small
volume of the phase space display parallax distributions which do not coincide
with the values from the literature. This is the result of ignoring a
possibility of assigning multiple probabilities to a single star. We propose
that this small number of clusters should be analysed anew.
