\DeclareSseqGroup \tower {} {
    \class(0,0)
    \DoUntilOutOfBounds {
        \class(\lastx,\lasty+1)
        \structline
    }
}

\begin{sseqdata}[ name = insert-example, y range = {0}{4}, class pattern = linear ]
\tower(0,2)
\tower(0,3)
\tower(0,1)
\end{sseqdata}
\qquad
\begin{sseqpage}[ name = insert-example ]
\tower[ red, classes = { insert = 1 } ](0,0)
\end{sseqpage}
\qquad
\begin{sseqpage}[ name = insert-example ]
\tower[ red, classes = { insert = 2 } ](0,0)
\end{sseqpage}
\qquad
\begin{sseqpage}[ name = insert-example ]
\tower[ red, classes = { insert = 3 } ](0,0)
\end{sseqpage}
\qquad
\begin{sseqpage}[ name = insert-example ]
\tower[ red, classes = { insert = -2 } ](0,0)
\end{sseqpage}
\qquad
\begin{sseqpage}[ name = insert-example ]
\tower[ red, classes = { insert = -3 } ](0,0)
\end{sseqpage}