How do I create a Tapered Extrusion?

Nhines31

Hi! I am very new to Onshape (a couple of weeks or so) and I am working on my second-ever project. My Christmas tree's plastic legs have been lost over many moves through the years and i wanted to use my new 3D printer to give the tree new legs to stand on instead of sending the whole thing to the trash. 

I have done my due diligence, watched many an hour of tutorials, read forums, and tinkered with tools in the software but I've hit a point where I don't really know what the right question is to ask. Or if I am even making proper drawings that can produce the part I'm looking for so I am turning to you for help (please go easy on me I am entirely new to CAD software as a whole and am learning as best I can).

Now that the pleasantries are out of the way. The true issue at hand. I created my sketch from a reference image on the Front plane. It consists of 3 shapes that I have proceeded to extrude to get me close to where I want to be (See Image 1*). 1 and 2 make up the slotted part that slides into the tree base to lock it in. 3 is the main part of the body, the structure. I extruded all 3 on a symmetrical plane per the dimensions i gathered with my calipers but realized from the top down the original part actually tapers from thick(noted by the yellow lines in image 2*), 15.5mm, to thin 9mm. But my extrusion is a consistent 15.5 all the way along the part. (See image 2*)

Do I have to create a plane on the top down with the thick-to-thin dimensions? If so how do I connect the 2 with the main body being a complex shape? As of right now because i sketched on the front face, when i look top down it's just a thin line. Obviously, if I started the sketch top down it would have been easier, but then I don't know how to get the complex body shape. I'm not really sure how to proceed. I am sure it's simple enough, I just can't seem to find the right video or explanation for exactly what I am encountering. 

I would greatly appreciate any help you can provide. Link to part: https://cad.onshape.com/documents/12170bbecb654fb285f3886d/w/3f0ac0e76483c3165f59b429/e/6e4a419db2cada72bce5b7e7

1*
 

2*

GWS50

Have a look at this
https://cad.onshape.com/documents/0500ee32d468fb9124d9d53c/w/bdc5730a07f6b095e8716bb7/e/03202082b8e8023955f3dac6

There are other ways to do this but this might give you a direction to go in

GWS50

Have a look at this
https://cad.onshape.com/documents/0500ee32d468fb9124d9d53c/w/bdc5730a07f6b095e8716bb7/e/03202082b8e8023955f3dac6

There are other ways to do this but this might give you a direction to go in

Nhines31

You are a Wizard! Thank you. Correct me if I am wrong but what you did was, instead of creating the extrusion as a taper from the beginning, you took what I did and then created a sketch on the bottom that you then subtracted from the extrusion. Thus creating the taper?