1. A method of generating a lexicon group tree, comprising the steps of: (a) generating, using at least one processor, a centroid lexicon representing lexicons belonging to a predetermined lexicon group; (b) selecting two lexicons, having a longest distance therebetween in the lexicon group, using the centroid lexicon from the lexicon group, and branching a node indicating the lexicon group, based on the two selected lexicons; and (c) selecting a node having low group similarity from among current terminal nodes, including branch nodes, and repeatedly performing steps (a) and (b) on a lexicon group indicated by the selected node, wherein the steps (a) and (b) are repeatedly performed until a variance, indicating group similarity, becomes lower than a predetermined threshold value and/or until the number of lexicons, belonging to a node, decreases to a predetermined number or less, and wherein the step (b) comprises the steps of: (b1) selecting a first lexicon having a longest distance to the centroid lexicon from the lexicon group; (b2) selecting a second lexicon having a longest distance to the first lexicon from the lexicon group; and (b3) bisecting remaining lexicons belonging to the lexicon group, based on the two selected lexicons.