Idea of Hierarchy Icon
There is a small rounded square above three equally sized and shaped squares below it. There is a line connecting the top square directly to the one below and another line reaching from the top of the bottom left square crossing the middle line and connecting to the bottom right square.
This Hierarchy 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 6,100 icons, all in the same style and quality.