There are a number of ways that you can do this. Have fun with this part of the project!  Build a rope ladder Build a ladder using 2 12-foot 2x4s and 2 8-foot 2x3s. Place the 2x4s side by side in perfect symmetry, marking off where each rung should go. Cut out 2x3 notches about 1 1⁄8 inches (2.9 cm) deep into both sides of the 2x4s. Cut the 2x3s the appropriate length for rungs and glue them into their notches with wood glue. Secure your rungs with deck screws and wait for the glue to dry. Stain your ladder to give it a nice hue and protect it from the elements. This roof is made from a simple tarp, although you can also get more elaborate in designing and constructing your roof. Drive one hook into both trunks about 8 feet (2.4 m) above the bottom of the platform. String a bungee cord between the two hooks and slip a tarp overhead. Next, build four outriggers several feet high and attach them to the four corners of your railing. Nail the tarp to the four corners of the outriggers, securing with a washer. Now your roof should have a better overhang. If you want to weatherproof your treehouse, or just give it a more appealing look, now's the time to stain or paint it. Consider a stain or paint that will work in combination with your house.

TL;DR in Chinese:
做好通向树屋的梯子，并把梯子固定在树屋地板上。 给你的树屋加上简单的屋顶。 给树屋上色。