One can easily invest in Tetra Tech Inc shares from India by:
Direct Investment - Opening an international trading account with Groww which includes KYC verification in the US. Your account gets activated in a few minutes to a few hours, after which you can start adding funds in USD balance to buy Tetra Tech Inc shares.
Indirect Investment - Under this form of investment, you can choose either a Mutual Fund (MF) or an Exchange-Traded Fund (ETF) that invests in global shares and start investing in shares of Tetra Tech Inc.