I recently started with bonsai, I got a few trees now. Obviously I am going to take branches of my trees. I though why not stick them in some soil and see if I get some to root. I already have rooting hormone anyway but I wonder about the soil. Should I just use the same mixture as the parent tree? Maybe smaller size. Or should I use normal potting soil and a layer of pumice on the bottom for draining. Also, what container. I have pondbaskets now, or should I use normal seed baskets(less draining and air)

branches will not root. If you want cuttings then take them at the appropriate time of the year, not now. Cuttings are usually quite short and not very thick. It also depends on the species. Many species will not root from cuttings.

rogerchipman wrote: I recently started with bonsai, I got a few trees now. Obviously I am going to take branches of my trees. I though why not stick them in some soil and see if I get some to root. I already have rooting hormone anyway but I wonder about the soil. Should I just use the same mixture as the parent tree? Maybe smaller size. Or should I use normal potting soil and a layer of pumice on the bottom for draining. Also, what container. I have pondbaskets now, or should I use normal seed baskets(less draining and air)

slope game

Every species is slightly different and the exact cutting process varies. Some do cuttings in spring, some in fall. Read the care guides.

For some reason I decided to read Robinson Crusoe. In it he cuts some treea and tree branches, sticks them in the ground to form a stockade, and they all take root, grow to expand the stockade, and form a canopy for birds to nest in. I laughed. 

I do the same as you. I put everything I cut into soil and sees what works and not.

Generally speaking cuttings work better in more heavy soil mix than established trees.

I have good success with taking authum cuttings when kept frost free during winter.

But as previous posters suggests, every species vary. Some are great to take cuttings from year round, some need a specific time and some is impossible.