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 Greentech icon is made in Material Design style
developed by Google. This style is based on extremely simplified shapes, thin two-pixel lines, and is optimized for 24x24 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 6,000 icons, all in the same style and quality.