Hmmm... maybe try thinking of the tree shape on its own first, bare, with just the branches. Like how u would draw a person, or an animal, if they were wearing clothes. U'll have an easier time if u draw the base of the figure before u add the extras on. :
Then add the leaves. Remember how small the leaves are compared to the tree; u'd want to draw them as a mass, yet keep all those little leaves still defined to some extent.
If it helps, you can think of the the leaves like a mass of feathers, or like clouds. That might help u get an idea of its form better.
It also helps a lot to look at a real-life picture of (pine) trees.
don't be afraid of going dark and remember where shadows appear. Keep in mind the tree is a 3-D shape, so some parts will be further away and in the shade more. i know it's messy, but... hm, here's what i did. >< :
Be careful also not to highlight too much, or make the highlights too smooth. Trees aren't usually very reflective.
i hope i helped u. >< >< >3< Maybe this'll make drawing trees less of a weak point for u.