Introduction Sequence

Up she rises

Up She Rises, the first video in the introduction

Hero's horrifying Tree experience in "Branches."

The introduction sequence includes all videos from "Up She Rises," to "Just a Mark." I highly reccomend watching the videos before reading the text next to them, in order to avoid spoilers.

Overview of Introduction

The introduction to the series is what sets the stage for the first plot arc.  The introduction includes 

• A car ride with Hero and his brother
• A phone call between Hero and his friend Alex
• A first obvious encounter with Hero and the Treeman
• A horrifying Tree experience
• An unlisted video that hints at a point much later in the story
• A "series end," which is soon revealed to be a lie.

The introduction also hints at the M.E.E.C, and contains the classic MarbleHornets refrence with "Alex"

Video by Video

1. Up She Rises. This introduction to the introduction includes the basic goal of Hero, to uncover the "Riddle of the Treeman."  There is also a House of Paradox (creators previous series) reference, and a brief, almost impossible to notice sighting of the Treeman.  
2. Alex.  This second video goes more in depth into the Mark on Hero's arm.  This is the obvious MarbleHornets reference, and several interesting things occur.  One of them being the blood on Hero's hands before he actually touches the tree...hmmm, you can imagine what it could possibly mean. The "Narrarator," also makes himself obvious in the description.  He isn't all that important, but is an interesting way to make the series a little more third person, which there is a reason to.  There are also several subtle Treeman appearances.
3. //:Fox. This is the first obvious sighting of the Treeman there is also a strange noise accompanying the Treeman, which startles Hero, who initially thinks he is hearing a fox.  The M.E.E.C is the writer of this description, although you do not know who they are at this time.  
4. Branches. This horrifying occurence involves Hero's painful climb down from a tree he miraculously wakes up in.  It is highly speculated that the Treeman has moved Hero into the tree, as you can catch a glimpse of him moving away as the video starts.  After impaling his arm on a twig while grabbing his camera, Hero must pull it out, and cautiously make his way down the rather tall tree.  He later encounters the Treeman's trademark noise, and makes his way back inside.  
5. 128. This is an unlisted video that is written from the perspective of an unkown character. He warns Hero that "it will come tonight, and so will the other."  I will not give away what this means in this topic, but it comes into light later.
6. Just a Mark [End of Introduction]. Hero considers this his "last update," [obviously not] but nevertheless, creates this video.  Hero appears very troubled, as he drops his camera, and does not care at first.  The "stalkerman," as Hero calls him, appears in the background. In the next segment, you learn that Hero added this video in as an attempt to give up his quest. He also photoshopped the slenderman into the video.  

Speculation 

• The videos are being uploaded by someone other than Hero, hence the Narrarator descriptions
• Hero is not telling the truth (bloody hands in "Alex.")
•  Hero is insane and killed his brother? This is hinted at slightly with the paranoia comments in Alex, and the fact that his brother has gone missing in a matter of days not to mention the blood thing. This is even farther supported because of the cryptic 128 video.
• Hero added in the Treeman to his videos. He did it with the slenderman, who's to say he didn't do it with the Treeman?

Keep in mind that all of the speculation I have written is only speculation you could gather from these videos.  I won't spoil the story for you, is what I am saying.  Who knows what is true here?