This short demo outlines one way to quickly suggest a mass of ivy growing up a tree.
Draw in pencil and cover the whole area with a wash. The darker this wash the darker the ivy will be. Leave white or lighter areas depanding on the tone of ivy you want in the final painting.
Mix several greens of differing colours and tones and work these wet into wet in the area. Try not to leave hard edges and use a small brush to draw out colour to make random marks that stand for ivy leaves around the edge.
When the wash is dry use gouache with a small brush to add individual leaves and small branches. Paint the larger branches and trunk.
Tip: You can mix watercolour with white gouache to produce a pretty good opaque paint to use in place of individual gouache colours. Don’t use chinese white it won’t do the job.