It depends on what you mean by biggest. The tallest tree is a coast redwood (sequoia sempervirens) at 115m (379ft) tall, but that with the largest volume is the giant sequoia (sequoiadendron? giganteum), which has a more substantial trunk; the tree known as General Sherman contains an estimated 1,486 cubic metres (52,508 cubic feet) of timber.
The stoutest single trunk, though, belongs to the baobab (adansonia digitata), the biggest of which had a diameter of 15.9m (52.1ft). Some trees such as the UK native aspen (populus tremula) produce suckers so that a whole forest might just be one individual. You can age some trees by their rings, but only trees which grow in seasonal climates produce them and even then decay of the heartwood in the centre means finding an age isn’t always possible. The great basin bristlecone pine (pinus longaeva) is the oldest verified by tree ring counts, at 4,844 years.? Dr. Fred Rumsey, Department of Botany, Natural History Museum, London.