How do I create a tibble that has a column of tibbles or data.frames?

Question

# A tibble: 12 x 3
       x     y     z
   <dbl> <int> <int>
 1     1     1     2
 2     3     2     3
 3     2     3     4
 4     3     4     5
 5     2     5     6
 6     4     6     7
 7     5     7     8
 8     2     8     9
 9     1     9    10
10     1    10    11
11     3    11    12
12     4    12    13

The above is named df. It is one of ten tibbles that I want to store inside of:

t <- tibble(tbl=vector("list", 10))

If I do this:

t$tbl[1] <- df

or

t[1, 1] <- df

I get this warning message:

Warning message:
In t$tbl[1] <- df :
  number of items to replace is not a multiple of replacement length

and the output of

t$tbl[1]

is

[[1]]
 [1] 1 3 2 3 2 4 5 2 1 1 3 4