Investors will look back at 2020 as one of the most volatile years on record. We witnessed an incredibly fast descent in March: It took a mere 20 days for the Dow Jones to fall by more than 20% from its most recent high. The market then recovered starting later in the month, and as of this writing, all three major U.S. market indexes are up year to date. All this volatility could scare off many investors. But it's essential to remember that the market rewards patience. 

Long-term investors shouldn't be too concerned with how the market will behave over the next few months. Buying stocks that can perform well over the course of a decade or even longer is a better way to build wealth. In that spirit, here are two growth stocks that can triple over the next decade: Tandem Diabetes Care (TNDM -0.26%) and Square (SQ -0.34%). Let's find out why it's a great idea to add both to your portfolio.

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1. Tandem Diabetes Care

Diabetes is a serious chronic health condition that affects 34.2 million people in the U.S. alone, according to the U.S. Centers for Disease Control and Prevention. That number does not include the 88 million adults (one in three) who have prediabetes. What's more, the number of people diagnosed with diabetes is expected to increase in the coming years. Diabetes patients need all the help they can get to manage their illness. Tandem Diabetes Care provides them with one essential aspect of their care toolbox: insulin pumps. 

Tandem Diabetes' t:slim X2 insulin pump works in conjunction with Dexcom's G6 continuous glucose monitoring (CGM) system to continuously track and automatically adjust insulin levels. This product has been a hit with its target market, and Tandem Diabetes' revenue continues to grow at a good clip. During its second quarter ended on June 30, the company's sales jumped by 17% year over year to $109.2 million. This is after Tandem Diabetes' revenue climbed by 48% to $97.9 million during its first quarter that ended March 31.

Doctor holding a diabetes sign.

Image source: Getty Images.

For its fiscal year ending Dec. 31, 2019, the company's sales grew by 97% to $363.2 million. While Tandem Diabetes is still unprofitable, it is worth putting aside the bottom line for now and considering the company's prospects. It plans to have 500,000 customers by the end of 2024, up from 170,000 as of its second quarter. Tandem Diabetes argues it can reach this goal because there is a large market opportunity for its products -- both in the U.S. and abroad.

The company also prides itself as an innovator, and it has a pipeline with several potential products to better serve the needs of its customers. Thanks to these factors, Tandem Diabetes looks well-positioned to continue winning. The company's 93% gain on the market year to date is only the beginning, and within the next 10 years, this healthcare stock has the tools to triple -- or more. 

2. Square 

Square's original appeal was that it allowed small and medium-sized businesses to create makeshift payment processors on the fly. Thanks to the company's hardware and accompanying software, any electronic device could be turned into a point-of-sale (POS) solution. But Square offered much more than just POS; the company allowed business owners to focus on their operations by taking care of such services as inventory, payroll, loans, etc. Square's original business model has been a huge success, and investors have taken notice. The company's stock is up by more than 1,000% since its 2015 IPO. 

And while its ecosystem of sellers will remain a major strength, Square has branched out into other lines of business. Most notably, the company's person-to-person (P2P) payment app, Cash App, could be a key growth driver over the next decade. This isn't just because Cash App is a popular way to send money to family and friends. During Square's second quarter ended June 30, the app had more than 30 million monthly active customers, up from 24 million in December 2019.

Cashier swiping customer's card at a POS.

Image source: Getty Images.

More than simple payment transactions, Cash App offers various typical "banking" services such as a debit card, commission-free investing services (with the option to buy fractional shares), and direct deposits. The results of Square's Cash App speak for themselves.

During its second-quarter, which ended on June 30, Square's total net revenue was $1.92 billion, representing a 64% year-over-year increase. The company's gross profit was $597 million, 28% higher than the year-ago period. Cash App's revenue for the quarter came in at $1.20 billion, increasing 361% compared to last year's comparable period. The app's gross profit was $281 million, 167% higher than the prior-year quarter.

In other words, Cash App was responsible for much of Square's stellar growth during the second quarter. Investors can look forward to more of the same for many years to come. The company is merely scratching the surface of its market, both for its core business and Cash App. I'd be surprised if Square's stock does not triple in the coming decade.