  One regards spaces of trees as stratified spaces, to study distributions of
phylogenetic trees. Stratified spaces with may have cycles, however spaces of
trees with a fixed number of leafs are contractible. Spaces of trees with three
leafs, in particular, are spiders with three legs. One gives an elementary
proof of the stickiness of intrinsic sample means on spiders. One also
represents four leafs tree data in terms of an associated Petersen graph. One
applies such ideas to analyze RNA sequences of SARS-CoV-2 from multiple
sources, by building samples of trees and running nonparametric statistics for
intrinsic means on tree spaces with three and four leafs. SARS-CoV-2 are also
used to built trees with leaves consisting in addition to other related
coronaviruses.
