Your 1099-B could be long, particularly if you have frequent allocation changes or withdrawals. In particular, if you have enabled TLH+, you may see many transactions. What shows up as a single transaction in your activity section might actually be multiple ETF sales for tax purposes, which is what the 1099-B shows. Sales are grouped by date of sale. You can also reference your statements for a chronological list of transactions, each with a breakdown by ETF sold.
The CSV download of your 1099-B can also be useful to sort the information in different ways, or to import into other software. You can now generate a CSV download directly in your account.
Please note that Betterment is not a tax advisor and the information provided should not be construed as tax advice, but should be used for informational purposes only. Please consult a qualified tax professional or the IRS to determine the rules that apply to your individual tax situation.