Here is a good article on this. And here a good attempt to calculate the number of trees needed for a flight. There are some critical notes as well, summarized as follows:
"In the longer term, restoring the carbon storage function of ecosystems will be essential for reducing CO2. But tree planting is a slow and minor contributor to reducing greenhouse gases. The larger, more immediate need is to reduce emissions, primarily by reducing fossil fuel use and by drastically reducing land clearing and deforestation."
Bottom line: yes, tree planting can help to some degree, but as trees take many years to grow, and we need to reduce CO2 emissions now, reducing your travel miles is needed as well. That's why I prefer not to invest in start-ups that are located too far from home: the regular progress meetings would increase my carbon footprint too much. A promising start-up should be able to find angel investors close to home!