The key thing with any plant in a pot of compost is that the roots must get air (oxygen, actually). Overwatering is the most common error.
Stick your finger on the soil surface and drag it across the surface a short way. If it feels wet and soil sticks to your finger, you should not water. An alternative is to use a wooden skewer/stick/chop-stick. Shove it into the soil to the bottom of the pot. Periodically (say daily), pull it out and check that it is damp - water only when it isn't.
Of course, there will be problems if the soil gets too dry. When this happens, the leafs and young stems will suddenly be limp. You should then water and see them recover turgidity.
Likely you need to water less. I suggest that you not water until turgidity is lost and observe how the soil feels to your finger and/or the stick appears and feels. Then water ASAP - now you know.
Another thing to consider is the root temperature - the roots need to stay below 95F (35F). Put a meat thermometer probe in the soil amongst the roots and observe. You may need to cover the pot of soil with something (aluminum foil, a damp white towel, etc) to keep the roots from getting too hot.
The issue with growing a ginkgo in Mumbai is likely to be getting the necessary winter dormancy. Temperate trees all require something between 1,000 and 2,000 hours below 40F (5C). You may need to put the tree in a refrigerator to achieve this.