alt Hacker News> Forests, trees, and bipartite graphs are 2-colorable.
More precise: a graph is bipartite if and only if it is 2-colorable (this can actually be used as a definition).
Since forests are bipartite, and trees are forests, the other two statements follow.
Precisely! The reason I mentioned trees and forests are because they are probably more familiar.
The Bipartite graph class is also a bit silly in this case, since it's by definition the 2-colorable graphs: bipartite, or 2-partite are the graphs that can be partitioned into 2 (color)classes such that no edge is internally in a class.
More generally, the k-colorable graphs are exactly the k-partite graphs.