Draw the trunk for the tree, it can be whatever length you like.
Draw some circles at the bottom of the trunk. (This will be the starting point of the roots)
Draw some lines from the circles and lead them up the base of the trunk. (I erased the circles at this point)
Finish them off by making the end of the roots gradually smaller and maybe add some little extra roots on the side of the main roots.
Now for the top of the tree. For the top of the tree, draw two lines going outward from the trunk.
Then add lines simulating the branches branching out.
Add some on the side to make it more natural.
Then draw in the actual leaves by scribbling a type of circle shape on the top. The scribbling can be in puffy circles or in jagged lines.
Add in extra scribbles to make it appear more full and less empty.
Erase the branches that are above the leaves to make it more realistic.
This step is completely optional. If you want to add a hole in the tree, just draw a stretched out circle like seen above.
Then outline it to make it appear more realistic.
And you're done!