Why is the tree so yellow?

This happens when there is a deficiency of iron or magnesium. Epsom salt should be given for lack of magnesium. And iron deficiency usually occurs when the ph level of the soil increases. If the soil is alkaline, plants cannot absorb iron from the soil. You can use good vermicompost to acidify the soil, in that case you will get results after 1-2 months. You can use vinegar to get quick results.