How to visualize transactions within assets of a portfolio

I'm visualizing stock data, with the x-axis representing time and y-axis representing money. Now if a stock gains on value (because the share is more worth) the corresponding line moves up:

But how can I visualize transactions during time? Say I buy more shares throughout time, the graph shows a significant rise not caused by a well performing stock, but rather caused by the number of shares doubling:

Now I know technically, the graph is correct, but if I want to analyze stock performance the graph becomes useless as significant rises have no correspondence to actual performance.

Well, there are many ways to do that. For example, you can plot two lines on the same chart: gain per share on main y-axis and number of shares on secondary y-axis.

If your portfolio has several assets (as one could imply from the topic), you probably would want to show their weights/distribution in the portfolio. That you probably could achieve with stacked area chart or stacked bars.