The evolutionary tree of living things is currently supposed to run something along the lines of that listed below. Most of the tree was based on ideas from cladistics; where more than two groups are shown in a single branch, there is disagreement about how they diverged. Hypothetically taxonomy would follow the tree whenever possible, but in many places it does not at present.
The description as a "tree" results from earlier ideas of life as a progression from lower to higher forms. Although such views are discredited now, the imagery is too well established to be readily lost.