DCE is a standard compiler optimization that's been been around since at least the 80s. It's done in multiple different ways, and "tree shaking" is just one more way. Whether the term DCE is known doesn't seem relevant to what is the most descriptive and meaningful term for this optimization.

I can't speak to origins, but currently in the JS world DCE and tree-shaking refer to different things. "Tree-shaking" normally refers to when the bundler omits unreachable code, that a more naive bundler would have included. It's an oft-discussed topic because it wasn't possible to do in some earlier module formats, and some bundlers do it better than others. In this context the "tree" mostly refers to the dependency tree.

In contrast DCE usually refers what the JS engine does at runtime, via whatever means. But DCE isn't much discussed, unless one talking about v8 internals or the like.

DCE has been around at least since 1971 Frances E. Allen's "A catalogue of optimizing trasformations", but I don't have her earlier papers/internal ibm memos to be able to say, but the section on DCE in that paper didn't appear to contain any further references.