This appears to be a praying mantis egg case - likely a Chinese mantis specifically - and is harmless to the tree. While not a native species, they are firmly established in our area and are quite common. While you do not recall noticing it before, it was laid last autumn before the mother mantis died during freezing weather. She will lay the case on nearly any vertical (or sometimes not-so-vertical!) surface, typically high enough off the ground that foraging hungry mice won't discover them in the winter. The eggs overwinter in this protective case and hatch later in spring.

Miri