The tree gathered the mass from the environment.
Step-by-step explanation:
Trees are the producers of the environment who can undergo the process of photosynthesis. The process of photosynthesis involves the conversion of carbon dioxide and water chemically into glucose and oxygen in presence of sunlight. This glucose is then metabolized by the plant cells into different compounds like lipid, proteins, carbohydrate and different others. These compounds make up the plant body which makes the plant grow into much bigger plant. This makes the mass of the plant increase. Thus, the plant which was planted 10years ago gathered the mass from the environment and converted them into body building products which increased the plant mass by 250kgs.