Step 1: Draw the trunk as shown in the illustration. For simplicity, here I only use the Pen tool in AI, but if you want to have a dark light, gradient, and that, you can use Mesh and other advanced tools.
Step 2: Create a new layer (e.g Layer 1). In this new layer you draw a big heart to shape the tree. By the way you copy this big heart and scale it into 2 small hearts and fill them with red, pink gradient as shown in the image below.
Step 3: Go back to the last layer (background) to draw the branches. You should pay attention to distribute the branches evenly and do not go beyond the big heart-shaped.
Step 4: From 2 small hearts in the step 2, you copy them into many different hearts, scale them and paste inside the big heart. Hide Layer 1 (the layer with the big heart shape) and we have a very pretty heart shaped Valentine tree. Do not forget to add some flying hearts to make it more lively.
Step 5: Just add a few more details and wishes, then you will have a cute Valentine card to give your partner!
This tutorial is based on personal experience, so it is hard to avoid shortcomings, we look forward to receiving the support and suggestions from all of you!