In this paper, we consider 2.5D drawing of a pair of trees
which are connected by some edges,
representing relationships between nodes,
as an attempt to develop a tool
for analyzing pairwise hierarchical data.
We consider two ways of drawing such a graph,
called parallel and perpendicular drawings,
where the graph appears as a bipartite graph
viewed from two orthogonal angles $X$ and $Y$.
We define the occlusion of a drawing as the sum
of the edge crossings that can be seen in the two angles,
and propose algorithms to minimize the occlusion
based on the fundamental one-sided
crossing minimization problem.
We also give some visualization examples of our method
using phylogenetic trees and a mushroom database.