I have a Dataframe like this

data = [[1, [10, 11]], [1, [15, 16]], [2, [20, 24]], [2, [22, 23]]] 
df = pd.DataFrame(data, columns = ['id', 'val']) 

   id   val
0   1   [10, 11]
1   2   [15, 16]

Here length of each list in val is same.

I want to explode val row wise. I could not fine a direct way of doing it .
So as work around I used

df.explode('val')

Now I want to use df.pivot but before that I want to add column names for each id.
Something like this

    id  val col_name
0   1   10  col_1
0   1   11  col_2
1   2   15  col_1
1   2   16  col_2

How can I add col_name using groupby??
This will help me pivot the dataframe.
Also is there any direct way of explode row wise which looks like

id   col_1  col_2       
1   10      11
2   15      16