It is a small leaf inside of a lightbulb. The tip of the leaf is near the top of the lightbulb and the stem of the leaf reaches down to the bottom of the bulb.
This is a Greentech icon. We've made it in iOS style
, first introduced in iOS version 7 and supported in all later releases up until now (at least iOS 11). This style is based on thin two-pixel lines and is optimized for 50x50 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 13,300 icons, all in the same style and quality.