create hierarchies of quarter, months / Argument y must be a multivariate time series. Traceback:

Question

I have a time series dataframe A Time Series: 6 × 12 that can be generated by using following syntax

library(hts)
ts(rnorm(67),  start=c(2015, 4), frequency=12)

When I run

aggregate(ts(rnorm(67),  start=c(2015, 4), frequency=12), nfrequency=4)

It generates 'A Time Series: 6 × 4'

However, what I want to do is create hierarchies:

eg:

Level 0: 2015
Level 1: Q1, Q2, Q3, Q4
Level 2: January, February, ....December 

Where Q1= sum(January, February, March, April), Q2 = sum (next four months), etc.

when I run

hts(ts(rnorm(67),  start=c(2015, 4), frequency=12)) 

I get

Error: Argument y must be a multivariate time series.
Traceback:

1. hts(ts(rnorm(67), start = c(2015, 4), frequency = 12))
2. stop("Argument y must be a multivariate time series.", call. = FALSE)

So my goal is to obtain hierarchical values of annual data based on quarters and months, that is

Level 0: Total for that year
Level 1: Q1, Q2, Q3, Q4
Level 2: January, February, ....December