Importing render file to After Effect

Hi everyone, I´m creating a project. When I render animation, i saved with PNG type and frame rate:60fps. Now I have some problem that I need you help me. After I finished render, I go to Video Sequence Editor to add image and render to make movie. Then I import to After Effect but it has no alpha channel, so what kind of code do I have to use? However, when I add image(PNG with alpha channel) to After Effect but After Effect just get frame rate at 30fps.:eek: