Well, For newbies, I would recommend that you swing in a Pendulum like movement. For example, you first grapple, then swing to the left. Then when you get there, you swing to the right. That should propel you higher. Continue untill you get to around to the door of the treehouse. Then just repeat to get into the door. Grapple onto the building, swing up till your body touches the side of the building, but not the bottom.
There is another way, a more faster way, but it is alot harder and more dangerous.