Trick to append an object of class "phylo" to a "multiPhylo" object

I forgot about this trick. Objects of class "phylo" and "multiPhylo" have S3 combine methods; however when we want to append a object of class "phylo" to an object of class "multiPhylo" we run into a problem.

So for instance:

library(ape)
t1<-rtree(n=20)
t2<-rtree(n=20)
obj<-c(t1,t2)
obj

## 2 phylogenetic trees

## no problem!
## or
t1<-rmtree(n=20,N=10)
t2<-rmtree(n=100,N=2)
obj<-c(t1,t2)
obj

## 12 phylogenetic trees

## no problem!
## however:
t1<-rmtree(n=20,N=10)
t2<-rtree(n=20)
obj<-c(t1,t2)

## Error in `[<-.multiPhylo`(`*tmp*`, a:N, value = structure(list(edge = structure(c(21L, : at least one element in 'value' is not of class "phylo".

## doesn't work

A workaround that is not too hard is to make the "phylo" a "multiPhylo" object with one tree only, as follows:

t2<-list(t2)
class(t2)<-"multiPhylo"
t2

## 1 phylogenetic trees

obj<-c(t1,t2)
obj

## 11 phylogenetic trees

## works!