Suppose set s$1$ is $[1,2,5]$ and set s$2$ is $[2,3,6].$ After s$1.$addAll$($s$2),$ s$1$ is $\_\_\_\_\_\_\_\_\_\_.$

$[1,2,3,5,6]$

$[1,5]$

$[2]$

$[1,2,2,3,5,6]$