Using unity tree editor with blender trees I have made some low poly trees in blender render without the sapling add-on and the only problem is that when I import it to unity and add it to the tree editor and then place it on the terrain it only show half of the tree and the other half under the terrain.

NOTE the two trees in the back were manually placed and the two trees in the front were placed using tree editor and the materials for the trees are the standard

I want to know make the whole tree visible while still using the tree editor. I don't know if the problem is within unity or blender, help will be appreciated. 
Thanks in advanced.
Every object in Blender has a center point or origin for it's local coordinates in the 3D view

It is generally represented by a large orange dot by default. You have to have this into consideration when modeling.

Your tree's origin point is likely placed a the center or the tree instead of the trunk base.

Change this either by moving it's gemetry in edit mode so the center is at the bottom of the trunk, or place the 3D cursor where you want the center to be (for example select a face press Shift + S Cursor to Selection) and then exit Edit Mode and press Shift + Ctrl + Alt + C and choose Origin to 3D Cursor